Bump coverage from 5.4 to 5.5 (#176)

Bumps [coverage](https://github.com/nedbat/coveragepy) from 5.4 to 5.5.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@coverage-5.4...coverage-5.5)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -1,7 +1,7 @@
 black==20.8b1
 bumpversion==0.6.0
 cffi==1.14.5
-coverage==5.4
+coverage==5.5
 docutils==0.16
 flake8==3.8.4
 invoke==1.5.0