Allow Travis to install redis, and test gapipy's redis coverage

.travis.yml

@@ -8,7 +8,12 @@ python:
 sudo: false
 
 # command to install dependencies, e.g. pip install -r requirements.txt --use-mirrors
-install: pip install -r requirements-testing.txt
+install:
+  - pip install -r requirements-testing.txt
+  - pip install redis
 
 # command to run tests, e.g. python setup.py test
 script: python setup.py test
+
+services:
+  - redis