Run tests against python 3.5, 3.6, 3.7 and Django 1.11, 2.0 and 2.1

Author: Photonios

tox.ini

@@ -1,10 +1,11 @@
 [tox]
-envlist = py35-dj{111,20}
+envlist = py35-dj{111,20,21}, py36-dj{111,20,21}, py37-dj{111,20,21}
 
 [testenv]
 deps =
     dj111: Django>=1.11,<1.12
     dj20: Django>=2.0,<2.1
+    dj21: Django>=2.1,<2.2
     -rrequirements/test.txt
 setenv =
     DJANGO_SETTINGS_MODULE=settings