Fix the wrong css background url issue in production.css when the image located outside the jmvc root directory.

Fix the wrong css background url issue in production.css when the image located outside the jmvc root directory.

Issue: 
   jmvc/app/widget/widget.css   -----> "background: url(../../../image.png)"

In "jmvc/app/widget/production.css", I except '../../../image.png', but got '../../image.png' before the fix.