Bump coverage from 5.5 to 6.0.1

Bumps [coverage](https://github.com/nedbat/coveragepy) from 5.5 to 6.0.1.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@coverage-5.5...6.0.1)

---
updated-dependencies:
- dependency-name: coverage
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

requirements.txt

@@ -1,4 +1,4 @@
-coverage==5.5
+coverage==6.0.1
 Django==2.2.24
 django-debug-toolbar==3.2.2
 docutils==0.17.1