www/py-django-recaptcha: Update to 2.0.6

• Also switch to Django 2.2 (current LTS release) because Django 1.11 is End-of-Life.

• Use GitHub for a while as PyPI provides no sdist for the latest release.

Changelog:

https://github.com/praekelt/django-recaptcha/blob/2.0.6/CHANGELOG.rst

PR: 245309