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](coveragepy/coveragepy@coverage-5.3.1...coverage-5.4)

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

Author: dependabot-preview[bot]

test-requirements.txt

@@ -18,7 +18,7 @@ chardet==4.0.0
     # via requests
 contextlib2==0.6.0.post1
     # via -r test-requirements.in
-coverage==5.3.1
+coverage==5.4
     # via pytest-cov
 cssselect==1.1.0
     # via -r test-requirements.in