One more attempt to get the build to work on Django 1.8

.travis.yml

@@ -8,7 +8,7 @@ python:
 install:
   - pip install -e .
   - pip install -r tests/requirements.txt
-  - pip install https://github.com/django/django/archive/${DJANGO}.zip#egg=django
+  - pip install Django==${DJANGO}
 script: make test
 env:
   - DJANGO=1.4.20