title: SCSS mixin with argument interpolation is not working
body: <p>I'm creating a mixin to generate a CSS background gradient, per <a href="http://www.colorzilla.com/gradient-editor/" rel="nofollow">Ultimate CSS Gradient Generator</a>.</p>
  
  <p>The mixin looks like this:</p>
  
  <pre><code>@mixin gradient-2-colors($color-1, $color-1-pos, $color-2, $color-2-pos) {
    background: -moz-linear-gradient(top, $color-1 $color-1-pos, $color-2 $color-2-pos);
    ... [OTHER BROWSER-SPECIFIC ENTRIES]...
    filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='$color-1', endColorstr=\'$color-2\',GradientType=0 );
  }
  </code></pre>
  
  <p>and the last entry is giving me trouble, since <code>$color-1</code> in <code>startColorstr='$color-1'</code> is not being parsed as a variable! How can I escape this component of the mixin to make the variable work inside of quotes?</p>