Stop Postgresql before running on Travis

If we don't, we get an error when running chef, as we install another
postgres version.

.travis.yml

@@ -3,4 +3,5 @@ rvm:
   - 1.9.3
 before_install:
   - sudo gem install chef --no-ri --no-rdoc
+  - sudo service postgresql stop
 script: sudo chef-solo -c solo.rb -j solo.json