Fix errors when running tox locally.

Using Django>=1.7,<1.8 actually grabbed Django 1.8b. This specifies to
grab the version of Django that's less than 1.8a which will be the
latest of 1.7

tox.ini

@@ -89,25 +89,25 @@ deps =
 [testenv:py27-django17]
 basepython = python2.7
 deps =
-    Django>=1.7,<1.8
+    Django>=1.7,<1.8a
     {[testenv]deps}
 
 [testenv:py32-django17]
 basepython = python3.2
 deps =
-    Django>=1.7,<1.8
+    Django>=1.7,<1.8a
     {[testenv]deps}
 
 [testenv:py33-django17]
 basepython = python3.3
 deps =
-    Django>=1.7,<1.8
+    Django>=1.7,<1.8a
     {[testenv]deps}
 
 [testenv:py34-django17]
 basepython = python3.4
 deps =
-    Django>=1.7,<1.8
+    Django>=1.7,<1.8a
     {[testenv]deps}
 
 [testenv:flake8]