TravisCI environmenti run Redis 2.2 but we need Redis 2.4 to run the
integration tests in the test suite. For now we have simply disabled
the `connected` group of tests using a custom phpunit.xml file, we will
see later if it is worth building Redis on the fly with a `before_script`
directive in .travis.yml or just wait for a a new version of Redis to
be deployed on their VM images.
Daniele Alessandri