Update to Django 3.2

[cacoze]

[luzfcb]

This project is very easy to upgrade...

To a more bigger codebase, maybe django-codemod can help:

https://github.com/browniebroke/django-codemod/

pip install django-codemod
djcodemod run --deprecated-in 2.2 --deprecated-in 3.0 --deprecated-in 3.1 $(pwd)