This app now supports only actual Django (3.2 LTS, 4.0, 4.1) and Python (3.7+) versions.

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• Added Django 3.0 support.
• Dropped Django 2.1 support.
• Tested in Python 3.8.
• Added six as a dependency to support Django 1.11 on Python 2.7 and Django 3.0 simultaneously (https://docs.djangoproject.com/en/3.0/releases/3.0/#removed-private-python-2-compatibility-apis).