title: Wro4j : RubySassCss preprocessor is ignored
body: <p>I'm using wro4j 1.7.1 in a spring application. Recently I tried to add the RubySassCss preprocessor to the preprocessor I used but without any success.</p>
  
  <p>The configuration I used :</p>
  
  <pre><code># wro4j
  debug=true
  modelUpdatePeriod=0
  gzipResources=false
  disableCache=true
  preProcessors=rubySassCss
  # I tried also in post processing
  #postProcessors=rubySassCss
  managerFactoryClassName=com.workable.config.WroManager
  </code></pre>
  
  <p>It's not clear in the documentation which syntax I can use (scss or sass) so I have two files in a group :</p>
  
  <pre><code>&lt;group name="test"&gt;
      &lt;css&gt;/sass/example.sass&lt;/css&gt;
      &lt;css&gt;/sass/example.scss&lt;/css&gt;
  &lt;/group&gt;
  </code></pre>
  
  <p>When I display this group on a page (localhost/wro/test.css, I just see the content of those files without any processing :</p>
  
  <p>the sass file :    </p>
  
  <pre><code>=border-radius($radius)
   -webkit-border-radius:$radius
   -moz-border-radius:$radius
   -ms-border-radius:$radius
   border-radius:$radius
  </code></pre>
  
  <p>the scss file :</p>
  
  <pre><code>.box
   +border-radius(10px)@mixin border-radius($radius){-webkit-border-radius:$radius;-moz-border-radius:$radius;-ms-border-radius:$radius;border-radius:$radius;}.box{@include border-radius(10px);}.box{-webkit-border-radius:10px;-moz-border-radius:10px;-ms-border-radius:10px;border-radius:10px;}
  </code></pre>
  
  <p>any idea ?</p>