Update pytest from 4.5.0 to 4.6.1 (#650)

Author: pyup-bot

requirements-development.txt

@@ -8,7 +8,7 @@ flake8==3.7.7
 flake8-isort==2.7.0
 isort==4.3.20
 mock==3.0.5
-pytest==4.5.0
+pytest==4.6.1
 pytest-cov==2.7.1
 pytest-django==3.4.8
 pytest-factoryboy==2.0.2