update celery version (#639)

* testing

* update: celery supported version

* Update requirements/default.txt

---------

Co-authored-by: Asif Saif Uddin <[email protected]>

Author: kernelshard

requirements/default.txt

@@ -1 +1 @@
-celery>=3.1.15
+celery>=3.1.26,<4.1.0