Auto-update dependencies. [(#1355)](GoogleCloudPlatform/python-docs-samples#1355)

Author: dpebot

samples/appengine/flexible/tasks/requirements.txt

@@ -1,6 +1,6 @@
 Flask==0.12.2
 google-api-python-client==1.6.5
-google-auth==1.3.0
+google-auth==1.4.0
 google-auth-httplib2==0.0.3
 google-cloud-datastore==1.4.0
 gunicorn==19.7.1