Update django-grappelli to 2.13.4

[pyup-bot]

This PR updates django-grappelli from 2.13.3 to 2.13.4.

The bot wasn't able to find a changelog for this release. Got an idea?

Links

• PyPI: https://pypi.org/project/django-grappelli
• Changelog: https://pyup.io/changelogs/django-grappelli/
• Docs: http://django-grappelli.readthedocs.org

[coveralls]

Pull Request Test Coverage Report for Build 5546

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 75.806%

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Totals
Change from base Build 5538:	0.0%
Covered Lines:	3652
Relevant Lines:	4591

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💛 - Coveralls

[codecov-io]

Codecov Report

Merging #1354 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1354   +/-   ##
=======================================
  Coverage   75.21%   75.21%           
=======================================
  Files         117      117           
  Lines        4591     4591           
  Branches      562      562           
=======================================
  Hits         3453     3453           
  Misses        939      939           
  Partials      199      199

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[pyup-bot]

Closing this in favor of #1356