chore: tweak 'python_requires' to match supported Python versions (#114)

* chore: tweak 'python_requires' to match supported Python versions

Release-As: 1.24.0

* tests: drop Python 3.5 for unit tests
diff --git a/noxfile.py b/noxfile.py
index 3f01ef1..86758e1 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -71,13 +71,13 @@
         session.run(*pytest_args)
 
 
-@nox.session(python=["2.7", "3.5", "3.6", "3.7", "3.8", "3.9"])
+@nox.session(python=["2.7", "3.6", "3.7", "3.8", "3.9"])
 def unit(session):
     """Run the unit test suite."""
     default(session)
 
 
-@nox.session(python=["2.7", "3.5", "3.6", "3.7", "3.8", "3.9"])
+@nox.session(python=["2.7", "3.6", "3.7", "3.8", "3.9"])
 def unit_grpc_gcp(session):
     """Run the unit test suite with grpcio-gcp installed."""
 
diff --git a/setup.py b/setup.py
index baea1c0..576363a 100644
--- a/setup.py
+++ b/setup.py
@@ -101,7 +101,7 @@
     namespace_packages=namespaces,
     install_requires=dependencies,
     extras_require=extras,
-    python_requires=">=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*",
+    python_requires=">=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,!=3.5.*",
     include_package_data=True,
     zip_safe=False,
 )