Test DRF versions up to DRF 3.6

This is the last DRF version to support Django 1.8, which is the
latest Django version which is included in the test matrix.

Author: kevin-brown

tox.ini

@@ -1,7 +1,9 @@
 [tox]
 envlist =
        py27-{flake8,docs},
-       {py27,py33,py34}-django{1.6,1.7,1.8}-drf{2.4,3.0,3.1}
+       {py27,py33,py34}-django1.6-drf{2.4,3.0,3.1,3.2}
+       {py27,py33,py34}-django1.7-drf{2.4,3.0,3.1,3.2,3.3}
+       {py27,py33,py34}-django1.8-drf{2.4,3.0,3.1,3.2,3.3,3.4,3.5,3.6}
 
 [testenv]
 commands = ./runtests.py --fast
@@ -14,6 +16,11 @@ deps =
        drf2.4: djangorestframework==2.4.4
        drf3.0: djangorestframework==3.0.5
        drf3.1: djangorestframework==3.1.3
+       drf3.2: djangorestframework==3.2.*
+       drf3.3: djangorestframework==3.3.*
+       drf3.4: djangorestframework==3.4.*
+       drf3.5: djangorestframework==3.5.*
+       drf3.6: djangorestframework==3.6.*
        pytest-django==2.8.0
 
 [testenv:py27-flake8]