tox: test against latest Django 1.11

Author: blueyed

tox.ini

@@ -18,7 +18,7 @@ deps =
     checkqa: flake8
 
     djangomaster: https://github.com/django/django/archive/master.tar.gz
-    django1.11: Django==1.11b1
+    django1.11: Django>=1.11,<1.12
     django1.10: Django>=1.10,<1.11
     django1.9: Django>=1.9,<1.10
     django1.8: Django>=1.8,<1.9