Update django-redis to 4.9.0

[pyup-bot]

There's a new version of django-redis available.
You are currently using 4.8.0. I have updated it to 4.9.0

These links might come in handy: PyPI | Changelog | Repo

Changelog

4.9.0

---

Date: 2018-03-01

• Add testing and support for Django 2.0. No actual code changes were required.
• Escape KEY_PREFIX and VERSION when used in glob expressions.
• Improve handling timeouts less than 1ms.
• Remove fakeredis support.
• Add datetime, date, time, and timedelta serialization support to the JSON
  serializer.
• The deprecated feature of passing True as a timeout value is no longer
  supported.
• Fix add() with a negative timeout to not store key (it is immediately
  invalid).
• Remove support for Django < 1.11.
• Add support for atomic incr if key is not set.

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖

[pyup-bot]

Closing this in favor of #443