Update django to 2.2.21

[pyup-bot]

This PR updates Django from 2.2.19 to 2.2.21.

Changelog

2.2.21

===========================

*May 4, 2021*

Django 2.2.21 fixes a security issue in 2.2.20.

CVE-2021-31542: Potential directory-traversal via uploaded files
================================================================

``MultiPartParser``, ``UploadedFile``, and ``FieldFile`` allowed
directory-traversal via uploaded files with suitably crafted file names.

In order to mitigate this risk, stricter basename and path sanitation is now
applied. Specifically, empty file names and paths with dot segments will be
rejected.


===========================

2.2.20

===========================

*April 6, 2021*

Django 2.2.20 fixes a security issue with severity "low" in 2.2.19.

CVE-2021-28658: Potential directory-traversal via uploaded files
================================================================

``MultiPartParser`` allowed directory-traversal via uploaded files with
suitably crafted file names.

Built-in upload handlers were not affected by this vulnerability.


===========================

Links

• PyPI: https://pypi.org/project/django
• Changelog: https://pyup.io/changelogs/django/
• Homepage: https://www.djangoproject.com/

[codecov]

Codecov Report

Merging #218 (ff58ecf) into master (a2f0d23) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #218   +/-   ##
=======================================
  Coverage   98.06%   98.06%           
=======================================
  Files          27       27           
  Lines        1293     1293           
=======================================
  Hits         1268     1268           
  Misses         25       25           

[pyup-bot]

Closing this in favor of #219