Update tox tests for modern Django combinations

Author: ben-xo

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = {py27,py33,py34}-django{17,18}
+envlist = {py27,py33,py34,py35,py36,py37}-django{17,18,19,110,111,20,21,22,30}
 
 [testenv]
 commands = py.test tests
@@ -10,7 +10,14 @@ setenv =
 deps =
     django17: Django>=1.7, <1.8
     django18: Django>=1.8, <1.9
-    pytest==2.6.4
+    django19: Django>=1.9, <1.10
+    django110: Django>=1.10, <1.11
+    django111: Django>=1.11, <2.0
+    {py33,py34,py35,py36,py37}-django20: Django>=2.0, <2.1
+    {py33,py34,py35,py36,py37}-django21: Django>=2.1, <2.2
+    {py33,py34,py35,py36,py37}-django22: Django>=2.2, <3.0
+    {py33,py34,py35,py36,py37}-django30: Django>=3.0, <3.1
+    pytest==4.6.7
     pytest-cov
     pytest-pep8
     pytest-flakes