Update pluggy to 0.5.1

[pyup-bot]

There's a new version of pluggy available.
You are currently using 0.5.0. I have updated it to 0.5.1

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

Changelog

0.5.1

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• fix a bug and add tests for case where firstresult hooks return
  None results. Thanks to RonnyPfannschmidt_ and tgoodlet
  for the issue (68) and PR (69) respectively.

.. _69: pytest-dev/pytest#69
.. _68: https://github.com/pytest-dev/pytest/issuses/68

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

Happy merging! 🤖

[codecov-io]

Codecov Report

Merging #104 into develop will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           develop   #104   +/-   ##
======================================
  Coverage      100%   100%           
======================================
  Files            4      4           
  Lines          136    136           
======================================
  Hits           136    136

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