Fix a few lint errors
diff --git a/google/auth/app_engine.py b/google/auth/app_engine.py
index 846bcec..ec89dc0 100644
--- a/google/auth/app_engine.py
+++ b/google/auth/app_engine.py
@@ -65,6 +65,9 @@
     Raises:
         EnvironmentError: If the App Engine APIs are unavailable.
     """
+    # pylint: disable=missing-raises-doc
+    # Pylint rightfully thinks EnvironmentError is OSError, but doesn't
+    # realize it's a valid alias.
     if app_identity is None:
         raise EnvironmentError(
             'The App Engine APIs are not available.')
@@ -92,6 +95,9 @@
         Raises:
             EnvironmentError: If the App Engine APIs are unavailable.
         """
+        # pylint: disable=missing-raises-doc
+        # Pylint rightfully thinks EnvironmentError is OSError, but doesn't
+        # realize it's a valid alias.
         if app_identity is None:
             raise EnvironmentError(
                 'The App Engine APIs are not available.')
diff --git a/google/auth/crypt.py b/google/auth/crypt.py
index 6151b29..1305cc8 100644
--- a/google/auth/crypt.py
+++ b/google/auth/crypt.py
@@ -204,7 +204,7 @@
             key_id (str): An optional key id used to identify the private key.
 
         Returns:
-            ~google.auth.crypt.Signer: The constructed signer.
+            google.auth.crypt.Signer: The constructed signer.
 
         Raises:
             ValueError: If the key cannot be parsed as PKCS#1 or PKCS#8 in
@@ -242,7 +242,7 @@
                 format.
 
         Returns:
-            ~google.auth.crypt.Signer: The constructed signer.
+            google.auth.crypt.Signer: The constructed signer.
 
         Raises:
             ValueError: If the info is not in the expected format.
@@ -265,7 +265,7 @@
             filename (str): The path to the service account .json file.
 
         Returns:
-            ~google.auth.crypt.Signer: The constructed signer.
+            google.auth.crypt.Signer: The constructed signer.
         """
         with io.open(filename, 'r', encoding='utf-8') as json_file:
             data = json.load(json_file)
diff --git a/google/auth/transport/grpc.py b/google/auth/transport/grpc.py
index 4062972..e6a5eb7 100644
--- a/google/auth/transport/grpc.py
+++ b/google/auth/transport/grpc.py
@@ -33,6 +33,10 @@
             object used to refresh credentials as needed.
     """
     def __init__(self, credentials, request):
+        # pylint: disable=no-value-for-parameter
+        # pylint doesn't realize that the super method takes no arguments
+        # because this class is the same name as the superclass.
+        super(AuthMetadataPlugin, self).__init__()
         self._credentials = credentials
         self._request = request
 
diff --git a/scripts/run_pylint.py b/scripts/run_pylint.py
index b06a98c..e9ac7ec 100644
--- a/scripts/run_pylint.py
+++ b/scripts/run_pylint.py
@@ -43,6 +43,7 @@
             'protected-access',
             'redefined-variable-type',
             'similarities',
+            'no-else-return',
         ],
     },
 }