chore: blacken (#375)

diff --git a/google/oauth2/service_account.py b/google/oauth2/service_account.py
index c60c565..17fdd51 100644
--- a/google/oauth2/service_account.py
+++ b/google/oauth2/service_account.py
@@ -82,9 +82,7 @@
 _DEFAULT_TOKEN_LIFETIME_SECS = 3600  # 1 hour in seconds
 
 
-class Credentials(credentials.Signing,
-                  credentials.Scoped,
-                  credentials.Credentials):
+class Credentials(credentials.Signing, credentials.Scoped, credentials.Credentials):
     """Service account credentials
 
     Usually, you'll create these credentials with one of the helper
@@ -116,8 +114,16 @@
         delegated_credentials = credentials.with_subject(subject)
     """
 
-    def __init__(self, signer, service_account_email, token_uri, scopes=None,
-                 subject=None, project_id=None, additional_claims=None):
+    def __init__(
+        self,
+        signer,
+        service_account_email,
+        token_uri,
+        scopes=None,
+        subject=None,
+        project_id=None,
+        additional_claims=None,
+    ):
         """
         Args:
             signer (google.auth.crypt.Signer): The signer used to sign JWTs.
@@ -169,9 +175,11 @@
         """
         return cls(
             signer,
-            service_account_email=info['client_email'],
-            token_uri=info['token_uri'],
-            project_id=info.get('project_id'), **kwargs)
+            service_account_email=info["client_email"],
+            token_uri=info["token_uri"],
+            project_id=info.get("project_id"),
+            **kwargs
+        )
 
     @classmethod
     def from_service_account_info(cls, info, **kwargs):
@@ -190,7 +198,8 @@
             ValueError: If the info is not in the expected format.
         """
         signer = _service_account_info.from_dict(
-            info, require=['client_email', 'token_uri'])
+            info, require=["client_email", "token_uri"]
+        )
         return cls._from_signer_and_info(signer, info, **kwargs)
 
     @classmethod
@@ -206,7 +215,8 @@
                 credentials.
         """
         info, signer = _service_account_info.from_filename(
-            filename, require=['client_email', 'token_uri'])
+            filename, require=["client_email", "token_uri"]
+        )
         return cls._from_signer_and_info(signer, info, **kwargs)
 
     @property
@@ -237,7 +247,8 @@
             token_uri=self._token_uri,
             subject=self._subject,
             project_id=self._project_id,
-            additional_claims=self._additional_claims.copy())
+            additional_claims=self._additional_claims.copy(),
+        )
 
     def with_subject(self, subject):
         """Create a copy of these credentials with the specified subject.
@@ -256,7 +267,8 @@
             token_uri=self._token_uri,
             subject=subject,
             project_id=self._project_id,
-            additional_claims=self._additional_claims.copy())
+            additional_claims=self._additional_claims.copy(),
+        )
 
     def with_claims(self, additional_claims):
         """Returns a copy of these credentials with modified claims.
@@ -280,7 +292,8 @@
             token_uri=self._token_uri,
             subject=self._subject,
             project_id=self._project_id,
-            additional_claims=new_additional_claims)
+            additional_claims=new_additional_claims,
+        )
 
     def _make_authorization_grant_assertion(self):
         """Create the OAuth 2.0 assertion.
@@ -296,20 +309,20 @@
         expiry = now + lifetime
 
         payload = {
-            'iat': _helpers.datetime_to_secs(now),
-            'exp': _helpers.datetime_to_secs(expiry),
+            "iat": _helpers.datetime_to_secs(now),
+            "exp": _helpers.datetime_to_secs(expiry),
             # The issuer must be the service account email.
-            'iss': self._service_account_email,
+            "iss": self._service_account_email,
             # The audience must be the auth token endpoint's URI
-            'aud': self._token_uri,
-            'scope': _helpers.scopes_to_string(self._scopes or ())
+            "aud": self._token_uri,
+            "scope": _helpers.scopes_to_string(self._scopes or ()),
         }
 
         payload.update(self._additional_claims)
 
         # The subject can be a user email for domain-wide delegation.
         if self._subject:
-            payload.setdefault('sub', self._subject)
+            payload.setdefault("sub", self._subject)
 
         token = jwt.encode(self._signer, payload)
 
@@ -318,8 +331,7 @@
     @_helpers.copy_docstring(credentials.Credentials)
     def refresh(self, request):
         assertion = self._make_authorization_grant_assertion()
-        access_token, expiry, _ = _client.jwt_grant(
-            request, self._token_uri, assertion)
+        access_token, expiry, _ = _client.jwt_grant(request, self._token_uri, assertion)
         self.token = access_token
         self.expiry = expiry
 
@@ -379,8 +391,15 @@
         delegated_credentials = credentials.with_subject(subject)
 
     """
-    def __init__(self, signer, service_account_email, token_uri,
-                 target_audience, additional_claims=None):
+
+    def __init__(
+        self,
+        signer,
+        service_account_email,
+        token_uri,
+        target_audience,
+        additional_claims=None,
+    ):
         """
         Args:
             signer (google.auth.crypt.Signer): The signer used to sign JWTs.
@@ -424,8 +443,8 @@
         Raises:
             ValueError: If the info is not in the expected format.
         """
-        kwargs.setdefault('service_account_email', info['client_email'])
-        kwargs.setdefault('token_uri', info['token_uri'])
+        kwargs.setdefault("service_account_email", info["client_email"])
+        kwargs.setdefault("token_uri", info["token_uri"])
         return cls(signer, **kwargs)
 
     @classmethod
@@ -445,7 +464,8 @@
             ValueError: If the info is not in the expected format.
         """
         signer = _service_account_info.from_dict(
-            info, require=['client_email', 'token_uri'])
+            info, require=["client_email", "token_uri"]
+        )
         return cls._from_signer_and_info(signer, info, **kwargs)
 
     @classmethod
@@ -461,7 +481,8 @@
                 credentials.
         """
         info, signer = _service_account_info.from_filename(
-            filename, require=['client_email', 'token_uri'])
+            filename, require=["client_email", "token_uri"]
+        )
         return cls._from_signer_and_info(signer, info, **kwargs)
 
     def with_target_audience(self, target_audience):
@@ -481,7 +502,8 @@
             service_account_email=self._service_account_email,
             token_uri=self._token_uri,
             target_audience=target_audience,
-            additional_claims=self._additional_claims.copy())
+            additional_claims=self._additional_claims.copy(),
+        )
 
     def _make_authorization_grant_assertion(self):
         """Create the OAuth 2.0 assertion.
@@ -497,15 +519,15 @@
         expiry = now + lifetime
 
         payload = {
-            'iat': _helpers.datetime_to_secs(now),
-            'exp': _helpers.datetime_to_secs(expiry),
+            "iat": _helpers.datetime_to_secs(now),
+            "exp": _helpers.datetime_to_secs(expiry),
             # The issuer must be the service account email.
-            'iss': self.service_account_email,
+            "iss": self.service_account_email,
             # The audience must be the auth token endpoint's URI
-            'aud': self._token_uri,
+            "aud": self._token_uri,
             # The target audience specifies which service the ID token is
             # intended for.
-            'target_audience': self._target_audience
+            "target_audience": self._target_audience,
         }
 
         payload.update(self._additional_claims)
@@ -518,7 +540,8 @@
     def refresh(self, request):
         assertion = self._make_authorization_grant_assertion()
         access_token, expiry, _ = _client.id_token_jwt_grant(
-            request, self._token_uri, assertion)
+            request, self._token_uri, assertion
+        )
         self.token = access_token
         self.expiry = expiry