Bump coverage from 4.5.3 to 4.5.4

Bumps [coverage](https://github.com/nedbat/coveragepy) from 4.5.3 to 4.5.4.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](coveragepy/coveragepy@coverage-4.5.3...coverage-4.5.4)

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

Author: dependabot-preview[bot]

requirements-dev.txt

@@ -4,7 +4,7 @@ aiohttp-session==2.7.0
 aiohttp==3.5.4
 aiomysql==0.0.20
 aiopg==0.16.0
-coverage==4.5.3
+coverage==4.5.4
 docker==4.0.2
 flake8==3.7.8
 ipdb==0.12.1