Update pytest-cov from 2.6.1 to 2.7.1 (#618)

Author: pyup-bot

requirements-development.txt

@@ -9,7 +9,7 @@ flake8-isort==2.7.0
 isort==4.3.18
 mock==3.0.4
 pytest==4.4.1
-pytest-cov==2.6.1
+pytest-cov==2.7.1
 pytest-django==3.4.8
 pytest-factoryboy==2.0.2
 recommonmark==0.5.0