Try rbx-2 on travis
Try rbx-2 on travis

According to https://github.com/travis-ci/travis-ci/issues/2230#issuecomment-42742477, we should use rbx-2 for now.

mperrando/kaminari,parity/kaminari,Zhomart/kaminari,aelogica/kaminari,onursarikaya/kaminari,fkagami/kaminari,kaminari/kaminari,bsboris/kaminari,danimashu/kaminari,varvet/kaminari,iberianpig/kaminari,parity/kaminari,guodongme/kaminari,plribeiro3000/kaminari,guodongme/kaminari,sachin21/kaminari,dblock/kaminari,peter-umb/umbie_kaminari,wkirschbaum/kaminari,sr-education/kaminari,sideci-sample/sideci-sample-kaminari,epicagency/kaminari,mrstif/cursor,bonekost/kaminari,peter-umb/umbie_kaminari,amatsuda/kaminari,kaminari/kaminari,mrhead/kaminari,iberianpig/kaminari,mperrando/kaminari,royels/kaminari,aelogica/kaminari,thiagorp/kaminari,sendgrid/kaminari,epicagency/kaminari,Teino1978-Corp/Teino1978-Corp-kaminari,barkbox/cursor,wkirschbaum/kaminari,pat/kaminari,danimashu/kaminari,yui-knk/kaminari,plribeiro3000/kaminari,JuanitoFatas/kaminari,royels/kaminari,jiamaozheng/kaminari,Boomkat/kaminari,pat/kaminari,mrhead/kaminari,yui-knk/kaminari,sanrodari/kaminari,sanrodari/kaminari,antstorm/kaminari,thiagorp/kaminari,sendgrid/kaminari,Zhomart/kaminari,sachin21/kaminari,amatsuda/kaminari,bonekost/kaminari,varvet/kaminari,onursarikaya/kaminari,sendgrid/kaminari,joe1chen/kaminari,JuanitoFatas/kaminari,antstorm/kaminari,jiamaozheng/kaminari,joe1chen/kaminari,Boomkat/kaminari,dblock/kaminari,Teino1978-Corp/Teino1978-Corp-kaminari,sr-education/kaminari,bsboris/kaminari,jcoyne/kaminari