travis ci: Add PPA for SDL-2, which isn't in Ubuntu 12
travis ci: Add PPA for SDL-2, which isn't in Ubuntu 12

jbush001/NyuziProcessor,FulcronZ/NyuziProcessor,FulcronZ/NyuziProcessor,jbush001/NyuziProcessor,jbush001/NyuziProcessor,FulcronZ/NyuziProcessor,jbush001/NyuziProcessor,FulcronZ/NyuziProcessor,jbush001/NyuziProcessor,jbush001/NyuziProcessor