Celery: Update Celery to version 4.1.1

Upgrade Celery version used from 3.1.26 to 4.1.1. The following
settings have been renamed: CELERY_ALWAYS_EAGER to
CELERY_TASK_ALWAYS_EAGER, BROKER_URL to CELERY_BROKER_URL.

Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>

mayan/settings/testing/base.py

@@ -33,9 +33,8 @@ TEMPLATES[0]['OPTIONS']['loaders'] = (
     ),
 )
 
-CELERY_ALWAYS_EAGER = True
-CELERY_EAGER_PROPAGATES_EXCEPTIONS = True
-BROKER_BACKEND = 'memory'
+CELERY_TASK_ALWAYS_EAGER = True
+CELERY_TASK_EAGER_PROPAGATES = True
 
 # Remove middlewares not used for tests
 MIDDLEWARE = [