feat: add support for Python 3.10 (#284)

Fix new deprecation warning for 'threading.Condition.notifyAll'.
diff --git a/CONTRIBUTING.rst b/CONTRIBUTING.rst
index 6db668e..6b375f0 100644
--- a/CONTRIBUTING.rst
+++ b/CONTRIBUTING.rst
@@ -21,7 +21,7 @@
   documentation.
 
 - The feature must work fully on the following CPython versions:
-  3.6, 3.7, 3.8 and 3.9 on both UNIX and Windows.
+  3.6, 3.7, 3.8, 3.9, and 3.10 on both UNIX and Windows.
 
 - The feature must not add unnecessary dependencies (where
   "unnecessary" is of course subjective, but new dependencies should
@@ -71,7 +71,7 @@
 
 - To run a single unit test::
 
-    $ nox -s unit-3.9 -- -k <name of test>
+    $ nox -s unit-3.10 -- -k <name of test>
 
 
   .. note::
@@ -201,11 +201,13 @@
 -  `Python 3.7`_
 -  `Python 3.8`_
 -  `Python 3.9`_
+-  `Python 3.10`_
 
 .. _Python 3.6: https://docs.python.org/3.6/
 .. _Python 3.7: https://docs.python.org/3.7/
 .. _Python 3.8: https://docs.python.org/3.8/
 .. _Python 3.9: https://docs.python.org/3.9/
+.. _Python 3.10: https://docs.python.org/3.10/
 
 
 Supported versions can be found in our ``noxfile.py`` `config`_.
diff --git a/google/api_core/bidi.py b/google/api_core/bidi.py
index 56a021a..4b4963f 100644
--- a/google/api_core/bidi.py
+++ b/google/api_core/bidi.py
@@ -727,7 +727,7 @@
         """Resumes the response stream."""
         with self._wake:
             self._paused = False
-            self._wake.notifyAll()
+            self._wake.notify_all()
 
     @property
     def is_paused(self):
diff --git a/noxfile.py b/noxfile.py
index 6478bfd..617dc58 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -121,7 +121,7 @@
         session.run(*pytest_args)
 
 
-@nox.session(python=["3.6", "3.7", "3.8", "3.9"])
+@nox.session(python=["3.6", "3.7", "3.8", "3.9", "3.10"])
 def unit(session):
     """Run the unit test suite."""
     default(session)
diff --git a/setup.py b/setup.py
index 48c8979..d150bc0 100644
--- a/setup.py
+++ b/setup.py
@@ -87,6 +87,7 @@
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
         "Operating System :: OS Independent",
         "Topic :: Internet",
     ],