Update celery to 4.2.2

[pyup-bot]

This PR updates celery from 4.2.1 to 4.2.2.

Changelog

4.2.2

=====
:release-date: 2018-12-06 04:30 P.M IST
:release-by: Omer Katz

- Support both Redis client version 2.x and version 3.x.

Contributed by **Ash Berlin-Taylor** and **Jeppe Fihl-Pearson**

.. _version-4.2.1:

Links

• PyPI: https://pypi.org/project/celery
• Changelog: https://pyup.io/changelogs/celery/
• Homepage: http://celeryproject.org
• Docs: https://pythonhosted.org/celery/

[pyup-bot]

Closing this in favor of #61