Bump pytest-cov from 2.5.0 to 2.12.1

Bumps [pytest-cov](https://github.com/pytest-dev/pytest-cov) from 2.5.0 to 2.12.1.
- [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@v2.5.0...v2.12.1)

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

requirements-tests.txt

@@ -2,6 +2,6 @@ coverage==4.3.4
 pytest
 pytest-html==1.22.0
 pytest-dependency
-pytest-cov==2.5.0
+pytest-cov==2.12.1
 pytest-benchmark
 pytest-benchmark[histogram]