chore(deps): update dependency google-api-python-client to v2.21.0

Author: renovate-bot

samples/compute/requirements.txt

@@ -1,3 +1,3 @@
-google-api-python-client==2.20.0
+google-api-python-client==2.21.0
 google-auth==2.0.2
 google-auth-httplib2==0.1.0