chore: release 1.18.0 (#539)

* 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 22ac79c..6c68a75 100644
--- a/setup.py
+++ b/setup.py
@@ -32,7 +32,7 @@
 with io.open("README.rst", "r") as fh:
     long_description = fh.read()
 
-version = "1.17.2"
+version = "1.18.0"
 
 setup(
     name="google-auth",