Remove -webkit-gradient from the output CSS
Remove -webkit-gradient from the output CSS

According to https://github.com/visionmedia/nib/issues/94#issuecomment-19504293 the support for legacy -webkit-gradient has been dropped. This should be removed from the docs as well to avoid confusion.
ecmartinez/nib,ilovezy/nib,ilovezy/nib,tj/nib,F4-Group/nib,rstacruz/nib,ecmartinez/nib,seleckis/nib-pushup,seleckis/nib-pushup,F4-Group/nib,tj/nib,JulianWielga/stylus-less