Bump coverage from 4.5.1 to 5.4

Bumps [coverage](https://github.com/nedbat/coveragepy) from 4.5.1 to 5.4.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@coverage-4.5.1...coverage-5.4)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements.txt

@@ -3,7 +3,7 @@ jsonfield==2.0.2
 django-jsonview==2.0.0
 requests==2.22.0
 factory_boy==2.10.0
-coverage==4.5.1
+coverage==5.4
 psycopg2==2.7.4
 django-registration-redux==2.5
 djrill==2.1.0