add allow_failures to travis.yml for ruby-head and rails master
add allow_failures to travis.yml for ruby-head and rails master

zakuro9715/slim,JuanitoFatas/slim,raxoft/slim,etdev/slim,Nikeshsuwal/slim,sideci-sample/sideci-sample-slim,cheunghy/slim,raxoft/slim,yterajima/slim,fly19890211/slim,JuanitoFatas/slim,metallurgical/slim,ruijsun/slim,mojavelinux/slim,mojavelinux/slim,metallurgical/slim,slim-template/slim,Nikeshsuwal/slim,XueQian/slim,zakuro9715/slim,cheunghy/slim,slim-template/slim,ericboehs/slim,slim-template/slim,ruijsun/slim,fly19890211/slim,ericboehs/slim,XueQian/slim,etdev/slim