Test against multiple versions of Oscar and Django

To anticipate migrating to Oscar 1.1 and Django 1.8, let's run the
tests on Travis already.

Author: maiksprenger

.travis.yml

@@ -4,11 +4,16 @@ python:
   - "3.3"
   - "3.4"
 
+env:
+  global:
+    - PYTHONPATH=.:$PYTHONPATH
+  matrix:
+    - DJANGO=Django==1.7.8 OSCAR=django-oscar==1.0.2
+    - DJANGO=Django==1.7.8 OSCAR=django-oscar==1.1
+    - DJANGO=Django==1.8.2 OSCAR=django-oscar==1.1
+
 install:
-  - pip install 'django-oscar>=0.7'
+  - pip install $DJANGO $OSCAR
   - pip install -r requirements.txt
 
-env:
-  - PYTHONPATH=.:$PYTHONPATH
-
 script: py.test tests