Update pytest from 4.3.0 to 4.3.1 (#598)

Author: pyup-bot

requirements-development.txt

@@ -8,7 +8,7 @@ flake8==3.7.7
 flake8-isort==2.6.0
 isort==4.3.13
 mock==2.0.0
-pytest==4.3.0
+pytest==4.3.1
 pytest-cov==2.6.1
 pytest-django==3.4.8
 pytest-factoryboy==2.0.2