Bump coverage from 5.5 to 6.0

Bumps [coverage](https://github.com/nedbat/coveragepy) from 5.5 to 6.0.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@coverage-5.5...6.0)

---
updated-dependencies:
- dependency-name: coverage
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

pyproject.toml

@@ -33,7 +33,7 @@ yarl = ">=1.6.0"
 aresponses = "^2.1.4"
 black = "^21.9b0"
 blacken-docs = "^1.11.0"
-coverage = {version = "^5.5", extras = ["toml"]}
+coverage = {version = "^6.0", extras = ["toml"]}
 flake8 = "^3.9.1"
 flake8-docstrings = "^1.6.0"
 isort = "^5.9.3"