chore(deps): update dependency google-cloud-monitoring to v2.13.0 (#325)

Author: renovate-bot

privateca/snippets/requirements.txt

@@ -1,3 +1,3 @@
 google-cloud-private-ca==1.5.0
 google-cloud-kms==2.13.0
-google-cloud-monitoring==2.12.0
+google-cloud-monitoring==2.13.0