Bump pytest-cov from 2.12.1 to 3.0.0

Bumps [pytest-cov](https://github.com/pytest-dev/pytest-cov) from 2.12.1 to 3.0.0.
- [Release notes](https://github.com/pytest-dev/pytest-cov/releases)
- [Changelog](https://github.com/pytest-dev/pytest-cov/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest-cov@v2.12.1...v3.0.0)

---
updated-dependencies:
- dependency-name: pytest-cov
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

requirements.txt

@@ -3,6 +3,6 @@ pdoc3==0.10.0
 aiohttp>=3.6.1,<4.0
 aresponses==2.1.4
 pytest==6.2.5
-pytest-cov==2.12.1
+pytest-cov==3.0.0
 pytest-asyncio>=0.15.1
 backoff>=1.11.1