Bump coverage from 5.4 to 5.5

Bumps [coverage](https://github.com/nedbat/coveragepy) from 5.4 to 5.5.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](https://github.com/nedbat/coveragepy/compare/coverage-5.4...coverage-5.5)

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

requirements-docs.txt

@@ -93,7 +93,7 @@ click==7.1.2
     #   flask
 cloudflare==2.8.15
     # via -r requirements-docs.in
-coverage==5.4
+coverage==5.5
     # via -r requirements-tests.txt
 cryptography==3.4.6
     # via

requirements-tests.txt

@@ -42,7 +42,7 @@ click==7.1.2
     # via
     #   black
     #   flask
-coverage==5.4
+coverage==5.5
     # via -r requirements-tests.in
 cryptography==3.4.6
     # via