Add tests with DRF 3.3.x

Author: Mickaël Guérin

tox.ini

@@ -1,8 +1,11 @@
 [tox]
 envlist =
     django18-py{27,34,35}
+    django18-py{27,34,35}-drf33
     django19-py{27,34,35}
+    django19-py{27,34,35}-drf33
     django110-py{27,34,35}
+    django110-py{27,34,35}-drf33
     flake8
     isort-check
 skipsdist = True
@@ -16,6 +19,7 @@ deps =
     django18: Django>=1.8,<1.9
     django19: Django>=1.9,<1.10
     django110: Django>=1.10,<1.11
+    drf33: djangorestframework<3.4
     ; Requirements from demo project
     py27: mock
     -rdemo/requirements-demo.pip