Fixed: 2 integration problems with Travis CI

Before this fix:
 * Build PATH has recently changed on Travis CI and hard-coded values in `.travis.yml' were no more valid (the `builds` folder has been renamed as `build`)
 * Any contributor that forked the main project repository had to modify the definition of environment variables in order to integrate with http://travis-ci.org

With this fix cappuccino is correctly configured to be built on Travis CI and makes `.travis.yml` more generic (forkable).
Merge pull request #1728 from gildegoma/pr-forkable-travis-yml

Fixed: 2 integration problems with Travis CI