Update django-filter to 2.1.0

[pyup-bot]

This PR updates django-filter from 2.0.0 to 2.1.0.

Changelog

2.1

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

* Fixed a regression in ``FilterView`` introduced in 2.0. An empty ``QuerySet`` was
incorrectly used whenever the FilterSet was unbound (i.e. when there were
no GET parameters).  The correct, pre-2.0 behaviour is now restored.

A workaround was to set ``strict=False`` on the ``FilterSet``. This is no
longer necessary, so you may restore `strict` behaviour as desired.

* Added ``IsoDateTimeFromToRangeFilter``. Allows From-To filtering using
ISO-8601 formatted dates.

Links

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

[codecov]

Codecov Report

Merging #561 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #561   +/-   ##
======================================
  Coverage    95.6%   95.6%           
======================================
  Files          55      55           
  Lines        2843    2843           
======================================
  Hits         2718    2718           
  Misses        125     125

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