require gunicorn for GAE flex Cloud Tasks example (#1573)

bart-at-google · andrewsg · commit bf62fd639075 · 2018-07-17T11:30:05.000-07:00
Require gunicorn since it is used in the entrypoint.
diff --git a/appengine/flexible/tasks/requirements.txt b/appengine/flexible/tasks/requirements.txt
@@ -1,2 +1,3 @@
 Flask==0.12.2
+gunicorn==19.7.1
 google-cloud-tasks==0.2.0
