Added phantomjs 1.9.7 to the matrice 

As the new releases will be hosted on bitbucket, I think it's time to add the latest 1.9.x release.

With the hope the phantomjs core team will release the first 2.x release soon :) 

See http://phantomjs.org/download.html for information
Merge pull request #992 from mickaelandrieu/update-travis

Added phantomjs 1.9.7 to the matrice