chore: release 1.16.0 (#518)

* updated CHANGELOG.md [ci skip]

* updated setup.cfg [ci skip]

* updated setup.py

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>
diff --git a/setup.py b/setup.py
index 09bbcef..212228d 100644
--- a/setup.py
+++ b/setup.py
@@ -30,7 +30,7 @@
 with io.open("README.rst", "r") as fh:
     long_description = fh.read()
 
-version = "1.15.0"
+version = "1.16.0"
 
 setup(
     name="google-auth",