Refactored _background-image mixin. Fixes  issues. Works with Sass 3.1.8.
Refactored _background-image mixin. Fixes  issues. Works with Sass 3.1.8.

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