Edit the web process in the Procfile

Due to an indirect dependency issue for flower, the auth_email method
didn't work anymore. Therefore for the guides demonstration purposes,
the method was changed to the basic HTTP authentication with user:password.

Author: vioum

Procfile

@@ -1,2 +1,3 @@
-web: celery flower --port=$PORT --broker=$CLOUDAMQP_URL --auth=$FLOWER_AUTH_EMAIL
+web: celery flower --port=$PORT --broker=$CLOUDAMQP_URL
+--basic_auth=$FLOWER_AUTH_USER:$FLOWER_AUTH_PW
 worker: celery -A tasks worker --loglevel=info