Bump pytest-cov from 2.2.1 to 2.12.1

Bumps [pytest-cov](https://github.com/pytest-dev/pytest-cov) from 2.2.1 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@v2.2.1...v2.12.1)

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

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

Author: dependabot[bot]

requirements/rtd.txt

@@ -16,7 +16,7 @@ dnspython3==1.12.0
 py3dns==3.1.0
 mock==2.0.0
 pytest==2.9.1
-pytest-cov==2.2.1
+pytest-cov==2.12.1
 python-coveralls==2.7.0
 pep8==1.7.1
 git+https://github.com/SpamExperts/MINI-DNS-Server.git

requirements/tests.txt

@@ -1,7 +1,7 @@
 # Requirements for running tests.
 mock==2.0.0
 pytest==2.9.1
-pytest-cov==2.2.1
+pytest-cov==2.12.1
 python-coveralls==2.7.0
 pep8==1.7.1
 se_profile==1.0.0