Set Celery serialization to JSON only

mayan/settings/base.py

@@ -257,6 +257,9 @@ CELERY_TIMEZONE = 'UTC'
 CELERY_ENABLE_UTC = True
 CELERY_ALWAYS_EAGER = True
 CELERYBEAT_SCHEDULER = 'djcelery.schedulers.DatabaseScheduler'
+CELERY_ACCEPT_CONTENT = ['json']
+CELERY_TASK_SERIALIZER = 'json'
+CELERY_RESULT_SERIALIZER = 'json'
 # ------------ CORS ------------
 CORS_ORIGIN_ALLOW_ALL = True
 # ------ Django REST Swagger -----