Bump coverage from 5.0.3 to 5.0.4

Bumps [coverage](https://github.com/nedbat/coveragepy) from 5.0.3 to 5.0.4.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](coveragepy/coveragepy@coverage-5.0.3...coverage-5.0.4)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

test_requirements.txt

@@ -1,4 +1,4 @@
 pytest<6
 hypothesis<5.6.1
-coverage==5.0.3
+coverage==5.0.4
 attrs==19.3.0