add ruby-head for travis
add ruby-head for travis

eshimel/githug,legendtkl/githug,FP-QAs/githug,geoluther/githug,youyou22/githug,blueyi/githug,zachalewel/githug,jackmaney/githug,zachalewel/githug,blueyi/githug,Gazler/githug,geoluther/githug,Gazler/githug,kuramameng/githug,jackmaney/githug,HanJisoo/Test,HanJisoo/Test,hydrox24/githug,kaylal12/githug,Limags/githug,kuramameng/githug,HanJisoo/Test,eshimel/githug,raq929/githug,wrestt/githug,hydrox24/githug,jackmaney/githug,wrestt/githug,kaylal12/githug,resource11/githug,youyou22/githug,zachalewel/githug,raq929/githug,FP-QAs/githug,Limags/githug,hydrox24/githug,Limags/githug,legendtkl/githug,wrestt/githug,mtam2/githug,blueyi/githug,kaylal12/githug,legendtkl/githug,FP-QAs/githug,mtam2/githug,mtam2/githug,geoluther/githug,raq929/githug,resource11/githug,FP-QAs/githug,youyou22/githug,eshimel/githug,resource11/githug,Gazler/githug,kuramameng/githug