Cloning the right cakephp branch/tag for any given MAJOR.MINOR version and enabling tests on Travis.

That prevents us of having to update the travis file every time the master branch changes, or when a branch is removed.
Instead we can just have 2.0 which will be translated to the right ref, 2.0.6 tag in this case.
Merge pull request #14 from renan/travis-on-travis

Figure out what is the appropriate ref for any given MAJOR.MINOR semver