Update pytest-mock to 1.6.1

[pyup-bot]

There's a new version of pytest-mock available.
You are currently using 1.5.0. I have updated it to 1.6.1

These links might come in handy: PyPI | Changelog | Repo

Changelog

1.6.0

---

• The original assertions raised by the various Mock.assert_* methods
  now appear in the failure message, in addition to the message obtained from
  pytest introspection.
  Thanks quodlibetor_ for the initial patch (79_).

.. _quodlibetor: https://github.com/quodlibetor

.. _79: pytest-dev/pytest-mock#79

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖

[pyup-bot]

Closing this in favor of #100