www/py-django-bitfield: Update to 2.0.1

• Also assign the port to Django 2.2 (current LTS release) as Django 1.11 is End-of-Life.

• Sort variables a bit according to the PHB.

Changelog:

https://github.com/disqus/django-bitfield/blob/2.0.1/README.rst#changelog

PR: 245313
Approved by: maintainer timeout (14 days)