Update django-filter to 2.4.0

[pyup-bot]

This PR updates django-filter from 2.2.0 to 2.4.0.

Changelog

2.4.0

--------------------------

* SECURITY: Added a ``MaxValueValidator`` to the form field for
``NumberFilter``. This prevents a potential DoS attack if numbers with very
large exponents were subsequently converted to integers.

The default limit value for the validator is ``1e50``.

The new ``NumberFilter.get_max_validator()`` allows customising the used
validator, and may return ``None`` to disable the validation entirely.

* Added testing against Django 3.1 and Python 3.9.

In addition tests against Django main development branch are now required to
pass.

2.3.0

------------------------

* Fixed import of FieldDoesNotExist. (1127)
* Added testing against Django 3.0. (1125)
* Declared support for, and added testing against, Python 3.8. (1138)
* Fix filterset multiple inheritance bug (1131)
* Allowed customising default lookup expression. (1129)
* Drop Django 2.1 and below (1180)
* Fixed IsoDateTimeRangeFieldTests for Django 3.1
* Require tests to pass against Django `master`.

Links

• PyPI: https://pypi.org/project/django-filter
• Changelog: https://pyup.io/changelogs/django-filter/
• Repo: https://github.com/carltongibson/django-filter/tree/master

[pyup-bot]

Closing this in favor of #633