[WIP][RFC]  php-cs-fixer.phar to travis

This add to .travis.yml the execution of the CS fixer.
 
Adding the CS fixer will introduce a little bit of overhead in the travis job
 but I'm sure it will speed up the Pull Requests life-cycle of this repo.
Usually a PR get a lot of comments about CS.

To-do:

- [ ] PR header.
- [ ] improve the result adding a configuration file with an exclusion list.
- [ ] gather feedback about continue or not.

waiting feedback