Upgrade celery to avoid AtributeError:async
I was experimenting the same descrived here and this seems to be solution.
@@ -39,7 +39,7 @@ defusedxml==0.5.0
# Basic tools
redis==2.10.6
-celery==4.1.0
+celery==4.1.1
# django-allauth 0.33.0 dropped support for Django 1.9
# https://django-allauth.readthedocs.io/en/latest/release-notes.html#backwards-incompatible-changes
