Update celery requirements to its latest version

Upgrading celery requires to upgrade their dependencies as
well (kombu, redis). By using their latest version, it could help with
the random disconnection of the workers that we suffer sometimes.

After upgrading them all, the errors we have found when we pinned the
versions they all disappeared.

Author: humitos

requirements/pip.txt

@@ -30,15 +30,9 @@ pyyaml==5.1.2
 Pygments==2.4.2
 
 # Basic tools
-# Redis 3.x has an incompatible change and fails
-# https://stackoverflow.com/questions/53331405/django-compress-error-invalid-input-of-type-cachekey
-# https://github.com/sebleier/django-redis-cache/pull/162
-redis==2.10.6  # pyup: ignore
-# Kombu >4.3 requires redis>=3.2
-kombu==4.3.0  # pyup: ignore
-# Celery 4.2 is incompatible with our code
-# when ALWAYS_EAGER = True
-celery==4.1.1  # pyup: ignore
+redis==3.3.11
+kombu==4.6.7
+celery==4.3.0
 
 django-allauth==0.40.0