remove trailing comma from CELERY_ENABLE_UTC, a beat config option

To run beat after this, you must remove the celerybeat-schedule file from your notifications-api
project root

app/config.py

@@ -137,7 +137,7 @@ class Config(object):
         'visibility_timeout': 310,
         'queue_name_prefix': NOTIFICATION_QUEUE_PREFIX
     }
-    CELERY_ENABLE_UTC = True,
+    CELERY_ENABLE_UTC = True
     CELERY_TIMEZONE = 'Europe/London'
     CELERY_ACCEPT_CONTENT = ['json']
     CELERY_TASK_SERIALIZER = 'json'