Update pytest to 3.7.2 (#25)

This PR updates [pytest](https://pypi.org/project/pytest) from **3.7.1** to **3.7.2**.



<details>
  <summary>Changelog</summary>
  
  
   ### 3.7.2
   ```
   =========================

Bug Fixes
---------

- `3671 &lt;https://github.com/pytest-dev/pytest/issues/3671&gt;`_: Fix ``filterwarnings`` not being registered as a builtin mark.


- `3768 &lt;https://github.com/pytest-dev/pytest/issues/3768&gt;`_, `3789 &lt;https://github.com/pytest-dev/pytest/issues/3789&gt;`_: Fix test collection from packages mixed with normal directories.


- `3771 &lt;https://github.com/pytest-dev/pytest/issues/3771&gt;`_: Fix infinite recursion during collection if a ``pytest_ignore_collect`` hook returns ``False`` instead of ``None``.


- `3774 &lt;https://github.com/pytest-dev/pytest/issues/3774&gt;`_: Fix bug where decorated fixtures would lose functionality (for example ``mock.patch``).


- `3775 &lt;https://github.com/pytest-dev/pytest/issues/3775&gt;`_: Fix bug where importing modules or other objects with prefix ``pytest_`` prefix would raise a ``PluginValidationError``.


- `3788 &lt;https://github.com/pytest-dev/pytest/issues/3788&gt;`_: Fix ``AttributeError`` during teardown of ``TestCase`` subclasses which raise an exception during ``__init__``.


- `3804 &lt;https://github.com/pytest-dev/pytest/issues/3804&gt;`_: Fix traceback reporting for exceptions with ``__cause__`` cycles.



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

- `3746 &lt;https://github.com/pytest-dev/pytest/issues/3746&gt;`_: Add documentation for ``metafunc.config`` that had been mistakenly hidden.
   ```
   
  
</details>


 

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

requirements.txt

@@ -2,4 +2,4 @@ flake8==3.5.0
 httplib2==0.11.3
 jsonschema==2.6.0
 markdown-generator==0.1.3
-pytest==3.7.1
+pytest==3.7.2