Bump pytest-cov from 2.12.1 to 3.0.0 (#845)

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:development
  update-type: version-update:semver-major
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements_dev_optional.txt

@@ -15,7 +15,7 @@ pymongo==3.12.0
 tox==3.24.4
 coverage
 flake8==3.9.2
-pytest-cov==2.12.1
+pytest-cov==3.0.0
 pytest-doctestplus==0.11.0
 pytest-timeout==1.4.2
 h5py==3.4.0