add hhvm to travis ci config
add hhvm to travis ci config

leafo/scssphp,webdevid/scssphp,leafo/scssphp,dleffler/scssphp,kkkyyy03/scssphp,dleffler/scssphp,dleffler/scssphp,g105b/scssphp,webdevid/scssphp,webdevid/scssphp,g105b/scssphp,leafo/scssphp,g105b/scssphp