Update tox matrix to match agreed support

See #1 for the discussion

tox.ini

@@ -1,43 +1,29 @@
 [tox]
-envlist = py26-dj13, py27-dj14, py27-dj15, py27-dj16, py33-dj16
+envlist = py27-dj17, py27-dj18, py33-dj17, py33-dj18
-
-[testenv:py26-dj13]
-basepython = python2.6
-deps = 
-  south
-  django==1.3.5
-
-[testenv:py27-dj14]
-basepython = python2.7
-deps = 
-  south
-  django==1.4.3
-
-[testenv:py27-dj15]
-basepython = python2.7
-deps = 
-  south
-  django==1.5
-
-[testenv:py27-dj16]
-basepython = python2.7
-deps =
-  south
-  django==1.6
 
 [testenv:py27-dj17]
 basepython = python2.7
 deps =
   south
-  django==1.7rc2
+  django==1.7.8
 
-;south 1.0 is not python3 compatible, 0.8.4 was:
+[testenv:py27-dj17]
-;http://stackoverflow.com/questions/24529618/why-does-django-south-1-0-use-iteritems
+basepython = python2.7
-[testenv:py33-dj16]
+deps =
+  south
+  django==1.8.2
+  
+[testenv:py33-dj17]
 basepython = python3.3
 deps =
-  south==0.8.4
+  south
-  django==1.6
+  django==1.7.8
+
+[testenv:py33-dj17]
+basepython = python3.3
+deps =
+  south
+  django==1.8.2
 
 [testenv]
 commands =