Update pytest-cov to 2.12.0

[pyup-bot]

This PR updates pytest-cov from 2.11.1 to 2.12.0.

Changelog

2.12.0

-------------------

* Added coverage's `toml` extra to install requirements in setup.py.
Contributed by Christian Riedel in `410 <https://github.com/pytest-dev/pytest-cov/pull/410>`_.
* Fixed ``pytest_cov.__version__`` to have the right value (string with version instead of a string
including ``__version__ =``).
* Fixed license classifier in ``setup.py``.
Contributed by Chris Sreesangkom in `467 <https://github.com/pytest-dev/pytest-cov/pull/467>`_.
* Fixed *commits since* badge.
Contributed by Terence Honles in `470 <https://github.com/pytest-dev/pytest-cov/pull/470>`_.

Links

• PyPI: https://pypi.org/project/pytest-cov
• Changelog: https://pyup.io/changelogs/pytest-cov/
• Repo: https://github.com/pytest-dev/pytest-cov

[pyup-bot]

Closing this in favor of #226