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>

requirements.txt

@@ -210,9 +210,9 @@ flake8==3.7.5 \
 mock==2.0.0 \
     --hash=sha256:5ce3c71c5545b472da17b72268978914d0252980348636840bd34a00b5cc96c1 \
     --hash=sha256:b158b6df76edd239b8208d481dc46b6afd45a846b7812ff0ce58971cf5bc8bba
-pytest==4.2.0 \
-    --hash=sha256:6ac6d467d9f053e95aaacd79f831dbecfe730f419c6c7022cb316b365cd9199d \
-    --hash=sha256:65aeaa77ae87c7fc95de56285282546cfa9c886dc8e5dc78313db1c25e21bc07
+pytest==4.2.1 \
+    --hash=sha256:80cfd9c8b9e93f419abcc0400e9f595974a98e44b6863a77d3e1039961bfc9c4 \
+    --hash=sha256:c2396a15726218a2dfef480861c4ba37bd3952ebaaa5b0fede3fc23fddcd7f8c
 coverage==4.5.2 \
     --hash=sha256:06123b58a1410873e22134ca2d88bd36680479fe354955b3579fb8ff150e4d27 \
     --hash=sha256:09e47c529ff77bf042ecfe858fb55c3e3eb97aac2c87f0349ab5a7efd6b3939f \