feat(travis): add travis testing
fix(rename): shortened of #<File> has only a getter

Gulp use a new File object to ease pain of computing shortened names. The shortened is not settable. So I'm just creating a new File class.
See https://github.com/wearefractal/gulp/blob/dcaa92b965346c459b684e65779683bb006e9c8f/CHANGELOG.md#27