Update pytest to 3.7.3 (#337)

This PR updates [pytest](https://pypi.org/project/pytest) from **3.7.2** to **3.7.3**.



*The bot wasn't able to find a changelog for this release. [Got an idea?](https://github.com/pyupio/changelogs/issues/new)*

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

Author: pyup-bot

requirements.txt

@@ -411,9 +411,9 @@ zopfli==0.1.4 \
     --hash=sha256:df7f84a01c0d8c8936e764e63fd0478aa526dc405ee2ad437e633b28cf824141 \
     --hash=sha256:ea204478f5dd4b7c03ec8a25ac5512f5cd85b15e001724289d1676a52c4c1633 \
     --hash=sha256:f5d7840833608f1be3a5f928dbcc0a5ff45ebd8040ea6177864f61a72b773423
-pytest==3.7.2 \
-    --hash=sha256:3459a123ad5532852d36f6f4501dfe1acf4af1dd9541834a164666aa40395b02 \
-    --hash=sha256:96bfd45dbe863b447a3054145cd78a9d7f31475d2bce6111b133c0cc4f305118
+pytest==3.7.3 \
+    --hash=sha256:4abcd98faeea3eb95bd05aa6a7b121d5f89d72e4d36ddb0dcbbfd1ec9f3651d1 \
+    --hash=sha256:2e7c330338b2732ddb992217962e3454aa7290434e75329b1a6739cea41bea6b
 pytest-django==3.4.2 \
     --hash=sha256:2d2e0a618d91c280d463e90bcbea9b4e417609157f611a79685b1c561c4c0836 \
     --hash=sha256:59683def396923b78d7e191a7086a48193f8d5db869ace79acb38f906522bc7b