title: Using a function in Sass is returning the string containing the name of the function rather than the result
body: <p>I'm trying Zurb Foundation 5.</p>
  
  <p>So, I've created a new project and try changing settings. When I changed, for example, <code>$row-width: rem-calc(1170);</code> in my-project/scss/settings.scss, it compiled (in my-project/stylesheets/app.css) into:</p>
  
  <pre><code>.row {
    max-width: rem-calc(1170);
  }
  </code></pre>
  
  <p>It seems like it doesn't know about rem-calc function.
  How to make it calculate rem-calc properly?</p>