Bump celery from 3.1.18 to 5.2.2

Bumps [celery](https://github.com/celery/celery) from 3.1.18 to 5.2.2.
- [Release notes](https://github.com/celery/celery/releases)
- [Changelog](https://github.com/celery/celery/blob/master/Changelog.rst)
- [Commits](celery/celery@v3.1.18...v5.2.2)

---
updated-dependencies:
- dependency-name: celery
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,7 +1,7 @@
 amqp==1.4.9
 anyjson==0.3.3
 billiard==3.3.0.23
-celery==3.1.18
+celery==5.2.2
 certifi==2019.9.11
 chardet==3.0.4
 Django==2.2.28