Bump pytest-cov from 2.12.1 to 4.0.0

Bumps [pytest-cov](https://github.com/pytest-dev/pytest-cov) from 2.12.1 to 4.0.0.
- [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...v4.0.0)

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

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

Author: dependabot[bot]

poetry.lock

@@ -37,7 +37,7 @@ ipdb = "^0.13.2"
 mypy = "^0.812"
 flake8 = "^3.8.3"
 pytest = "^5.4.3"
-pytest-cov = "^2.10.0"
+pytest-cov = "^4.0.0"
 
 [tool.poetry.scripts]
 pybetter = 'pybetter.cli:main'