chore(deps): update dependency google-auth to v1.19.0 [(#4293)](GoogleCloudPlatform/python-docs-samples#4293)

Author: renovate-bot

samples/api-client/manager/requirements.txt

@@ -2,7 +2,7 @@ cryptography==2.9.2
 flaky==3.7.0
 google-api-python-client==1.9.3
 google-auth-httplib2==0.0.4
-google-auth==1.18.0
+google-auth==1.19.0
 google-cloud-iot==1.0.0
 google-cloud-pubsub==1.6.1
 paho-mqtt==1.5.0