Update pytest to 3.6.4

[pyup-bot]

This PR updates pytest from 3.6.3 to 3.6.4.

Changelog

3.6.4

=========================

Bug Fixes
---------

- Invoke pytest using ``-mpytest`` so ``sys.path`` does not get polluted by packages installed in ``site-packages``. (`742 <https://github.com/pytest-dev/pytest/issues/742>`_)


Improved Documentation
----------------------

- Use ``smtp_connection`` instead of ``smtp`` in fixtures documentation to avoid possible confusion. (`3592 <https://github.com/pytest-dev/pytest/issues/3592>`_)


Trivial/Internal Changes
------------------------

- Remove obsolete ``__future__`` imports. (`2319 <https://github.com/pytest-dev/pytest/issues/2319>`_)

- Add CITATION to provide information on how to formally cite pytest. (`3402 <https://github.com/pytest-dev/pytest/issues/3402>`_)

- Replace broken type annotations with type comments. (`3635 <https://github.com/pytest-dev/pytest/issues/3635>`_)

- Pin ``pluggy`` to ``<0.8``. (`3727 <https://github.com/pytest-dev/pytest/issues/3727>`_)

Links

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

[codecov-io]

Codecov Report

Merging #408 into master will increase coverage by 0.38%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #408      +/-   ##
==========================================
+ Coverage   75.09%   75.48%   +0.38%     
==========================================
  Files           5        5              
  Lines         779      779              
  Branches      227      227              
==========================================
+ Hits          585      588       +3     
+ Misses        138      137       -1     
+ Partials       56       54       -2

Impacted Files	Coverage Δ
tmuxp/workspacebuilder.py	90.9% <0%> (+1.81%)	⬆️

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[pyup-bot]

Closing this in favor of #410