chore(.travis.yml): fix for running tests with grunt
chore(.travis.yml): fix for running tests with grunt

twitwi/showdown,bsnizek/showdown,axter/showdown,showdownjs/showdown,OMGgogong/showdown,phw/showdown,snegovick/showdown,yaniswang/showdown,twitwi/showdown,webutilz/showdown,xinshitn/showdown,alazyer/showdown,stevemao/showdown,bsansouci/showdown,juanonsoftware/showdown,webutilz/showdown,OMGgogong/showdown,digideskio/showdown,xinshitn/showdown,alazyer/showdown,NichenLg/showdown,snegovick/showdown,bsnizek/showdown,NichenLg/showdown,axter/showdown,pazof/showdown,coolroad/showdown,showdownjs/showdown,stevemao/showdown,digideskio/showdown,yaniswang/showdown,phw/showdown,juanonsoftware/showdown,coolroad/showdown,bsansouci/showdown,pazof/showdown