Bump coverage from 5.0.3 to 5.3

Bumps [coverage](https://github.com/nedbat/coveragepy) from 5.0.3 to 5.3.
- [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-5.3)

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

Author: dependabot-preview[bot]

requirements_dev.txt

@@ -4,7 +4,7 @@ wheel==0.34.1
 watchdog==0.10.0
 flake8==3.7.9
 tox==3.14.3
-coverage==5.0.3
+coverage==5.3
 Sphinx==2.3.1
 cryptography==2.8
 PyYAML==5.3