add xvfb to travis config

this is required as some of our test require an X display (to start browser)
no need to test again node 0.8
remove useless quote
add compass install in travis config
using official angular bowser module
Chrome is not installed on travis. Trying with firefox
Merge pull request #1 from avernois/using_firefox_instead_of_chrome

Chrome is not installed on travis. Trying with firefox
Merge pull request #2 from avernois/setup_travis

Setup travis