Merge pull request #3745 from linovia/feature/py35_support

Fix tox build against python 3.5 by upgrading pytest.

Author: tomchristie

requirements/requirements-testing.txt

@@ -1,4 +1,4 @@
 # PyTest for running the tests.
-pytest==2.6.4
-pytest-django==2.8.0
+pytest==2.8.5
+pytest-django==2.9.1
 pytest-cov==1.8.1