Update pytest to 4.2.1
Update pytest to 4.2.1


This PR updates [pytest](https://pypi.org/project/pytest) from **4.2.0** to **4.2.1**.



<details>
  <summary>Changelog</summary>
  
  
   ### 4.2.1
   ```
   =========================

Bug Fixes
---------

- `2895 &lt;https://github.com/pytest-dev/pytest/issues/2895&gt;`_: The ``pytest_report_collectionfinish`` hook now is also called with ``--collect-only``.


- `3899 &lt;https://github.com/pytest-dev/pytest/issues/3899&gt;`_: Do not raise ``UsageError`` when an imported package has a ``pytest_plugins.py`` child module.


- `4347 &lt;https://github.com/pytest-dev/pytest/issues/4347&gt;`_: Fix output capturing when using pdb++ with recursive debugging.


- `4592 &lt;https://github.com/pytest-dev/pytest/issues/4592&gt;`_: Fix handling of ``collect_ignore`` via parent ``conftest.py``.


- `4700 &lt;https://github.com/pytest-dev/pytest/issues/4700&gt;`_: Fix regression where ``setUpClass`` would always be called in subclasses even if all tests
  were skipped by a ``unittest.skip()`` decorator applied in the subclass.


- `4739 &lt;https://github.com/pytest-dev/pytest/issues/4739&gt;`_: Fix ``parametrize(... ids=&lt;function&gt;)`` when the function returns non-strings.


- `4745 &lt;https://github.com/pytest-dev/pytest/issues/4745&gt;`_: Fix/improve collection of args when passing in ``__init__.py`` and a test file.


- `4770 &lt;https://github.com/pytest-dev/pytest/issues/4770&gt;`_: ``more_itertools`` is now constrained to &lt;6.0.0 when required for Python 2.7 compatibility.


- `526 &lt;https://github.com/pytest-dev/pytest/issues/526&gt;`_: Fix &quot;ValueError: Plugin already registered&quot; exceptions when running in build directories that symlink to actual source.



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

- `3899 &lt;https://github.com/pytest-dev/pytest/issues/3899&gt;`_: Add note to ``plugins.rst`` that ``pytest_plugins`` should not be used as a name for a user module containing plugins.


- `4324 &lt;https://github.com/pytest-dev/pytest/issues/4324&gt;`_: Document how to use ``raises`` and ``does_not_raise`` to write parametrized tests with conditional raises.


- `4709 &lt;https://github.com/pytest-dev/pytest/issues/4709&gt;`_: Document how to customize test failure messages when using
  ``pytest.warns``.



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

- `4741 &lt;https://github.com/pytest-dev/pytest/issues/4741&gt;`_: Some verbosity related attributes of the TerminalReporter plugin are now
  read only properties.
   ```
   
  
</details>


 

<details>
  <summary>Links</summary>
  
  - PyPI: https://pypi.org/project/pytest
  - Changelog: https://pyup.io/changelogs/pytest/
  - Homepage: https://docs.pytest.org/en/latest/
</details>


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