title: precompiling assets locally gives absolute url for background scss urls
body: <p>I am using heroku for my rails app. And I precompile assets locally and then deploy.
  So whenever I run
  <code> bundle exec rake assets:precompile</code></p>
  <p>my URLs in scss are converted from relative paths to absolute paths in precompiled scss so
  <code>/home.png</code> is converted to <code>http://localhost:3000/home.png</code></p>
  <p>How can I get relative paths in the precompiled files too?</p>