chore(travis): temporarily disable Firefox
chore(travis): temporarily disable Firefox

I can't get it allocated on SauceLabs and so this is failing all the builds, making our Travis build useless.

I contacted folks from SL. Once we figure it out, I will revert this change.
ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js