Simplify placeholder mixin
Simplify placeholder mixin

chriseppstein/bourbon,chriseppstein/bourbon,san650/bourbon,zyj1022/bourbon,Jazz-Man/bourbon,setie/bourbon,smithdamen/bourbon,Nikeshsuwal/bourbon,jasonwalkow/bourbon,greyhwndz/bourbon,jamadam/bourbon-docs-jp,jamesmenera/bourbon-libsass,greyhwndz/bourbon,jamadam/bourbon-docs-jp,thoughtbot/bourbon,jamesmenera/bourbon-libsass,mindeavor/bourbon,ismarkunc/bourbon,thoughtbot/bourbon,nagyistoce/sass-bourbon.io,setie/bourbon,jamadam/bourbon-docs-jp,jamadam/bourbon-docs-jp,mindeavor/bourbon,craftsmen/bourbon,craftsmen/bourbon,cllns/bourbon,smithdamen/bourbon,zyj1022/bourbon,Jazz-Man/bourbon,jasonwalkow/bourbon,nickg33/bourbon,nickg33/bourbon