Bump coverage from 5.4 to 5.5

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>

requirements.txt

@@ -3,7 +3,7 @@ certifi==2020.12.5
 chardet==4.0.0
 codecov==2.1.11
 configobj==5.0.6
-coverage==5.4
+coverage==5.5
 dpath==2.0.1
 google-auth==1.27.1
 httpretty==1.0.5