Bump django-filter from 2.1.0 to 2.2.0

Bumps [django-filter](https://github.com/carltongibson/django-filter) from 2.1.0 to 2.2.0.
- [Release notes](https://github.com/carltongibson/django-filter/releases)
- [Changelog](https://github.com/carltongibson/django-filter/blob/master/CHANGES.rst)
- [Commits](https://github.com/carltongibson/django-filter/compare/2.1.0...2.2.0

)

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

requirements.txt

@@ -11,7 +11,7 @@ django-basic-auth-ip-whitelist==0.3.1
 django-bleach==0.6.1
 django-countries==5.5
 django-extensions==2.1.7
-django-filter==2.1.0
+django-filter==2.2.0
 django-fsm==2.6.1
 django-heroku==0.3.1
 django-hijack==2.1.10