chore(deps-dev): bump coverage from 5.3.1 to 5.4

Bumps [coverage](https://github.com/nedbat/coveragepy) from 5.3.1 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-5.3.1...coverage-5.4)

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

dev-requirements.txt

@@ -1,4 +1,4 @@
-coverage==5.3.1
+coverage==5.4
 coveralls==1.7.0;python_version<'3.0'
 coveralls==2.2.0;python_version>='3.6'
 pytest==4.6.9;python_version<'3.0'