Update pytest to 3.7.1 (#24)

This PR updates [pytest](https://pypi.org/project/pytest) from **3.7.0** to **3.7.1**.



<details>
  <summary>Changelog</summary>
  
  
   ### 3.7.1
   ```
   =========================

Bug Fixes
---------

- `3473 &lt;https://github.com/pytest-dev/pytest/issues/3473&gt;`_: Raise immediately if ``approx()`` is given an expected value of a type it doesn&#39;t understand (e.g. strings, nested dicts, etc.).


- `3712 &lt;https://github.com/pytest-dev/pytest/issues/3712&gt;`_: Correctly represent the dimensions of an numpy array when calling ``repr()`` on ``approx()``.

- `3742 &lt;https://github.com/pytest-dev/pytest/issues/3742&gt;`_: Fix incompatibility with third party plugins during collection, which produced the error ``object has no attribute &#39;_collectfile&#39;``.

- `3745 &lt;https://github.com/pytest-dev/pytest/issues/3745&gt;`_: Display the absolute path if ``cache_dir`` is not relative to the ``rootdir`` instead of failing.


- `3747 &lt;https://github.com/pytest-dev/pytest/issues/3747&gt;`_: Fix compatibility problem with plugins and the warning code issued by fixture functions when they are called directly.


- `3748 &lt;https://github.com/pytest-dev/pytest/issues/3748&gt;`_: Fix infinite recursion in ``pytest.approx`` with arrays in ``numpy&lt;1.13``.


- `3757 &lt;https://github.com/pytest-dev/pytest/issues/3757&gt;`_: Pin pathlib2 to ``&gt;=2.2.0`` as we require ``__fspath__`` support.


- `3763 &lt;https://github.com/pytest-dev/pytest/issues/3763&gt;`_: Fix ``TypeError`` when the assertion message is ``bytes`` in python 3.
   ```
   
  
</details>


 

<details>
  <summary>Links</summary>
  
  - PyPI: https://pypi.org/project/pytest
  - Changelog: https://pyup.io/changelogs/pytest/
  - Repo: https://github.com/pytest-dev/pytest/issues
  - 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==3.7.0
+pytest==3.7.1