minor #175 use the container-based infrastructure on Travis (xabbuh)
minor #175 use the container-based infrastructure on Travis (xabbuh)

This PR was squashed before being merged into the master branch (closes #175).

Discussion
----------

use the container-based infrastructure on Travis

see http://blog.travis-ci.com/2014-12-17-faster-builds-with-container-based-infrastructure/ and http://docs.travis-ci.com/user/workers/container-based-infrastructure/

Commits
-------

7ddc37e use the container-based infrastructure on Travis

gabiudrescu/EasyAdminBundle,datagit/EasyAdminBundle,ogizanagi/EasyAdminBundle,yceruto/EasyAdminBundle,yceruto/EasyAdminBundle,alexgt9/EasyAdminBundle,kamilZ/EasyAdminBundle,datagit/EasyAdminBundle,alexgt9/EasyAdminBundle,thomasbeaujean/EasyAdminBundle,seydu/EasyAdminBundle,ogizanagi/EasyAdminBundle,datagit/EasyAdminBundle,thomasbeaujean/EasyAdminBundle,seydu/EasyAdminBundle,seydu/EasyAdminBundle,kamilZ/EasyAdminBundle,ogizanagi/EasyAdminBundle,gabiudrescu/EasyAdminBundle,yceruto/EasyAdminBundle,OskarStark/EasyAdminBundle,kamilZ/EasyAdminBundle,javiereguiluz/EasyAdminBundle,javiereguiluz/EasyAdminBundle,thomasbeaujean/EasyAdminBundle,OskarStark/EasyAdminBundle,alexgt9/EasyAdminBundle,ogizanagi/EasyAdminBundle,OskarStark/EasyAdminBundle,gabiudrescu/EasyAdminBundle