title: Functions may not be defined within control directives other mixins
body: <p>I have a node project and when i start the command line npm install, i have this error :</p>
  
  <p>Message:
      node_modules\compass-mixins\lib\compass\functions_lists.scss
  Error: Functions may not be defined within control directives or other mixins.
          on line 81 of node_modules/compass-mixins/lib/compass/functions/_lists.scss</p>
  
  <blockquote>
    <blockquote>
      <p>@function compact($vars...) {</p>
    </blockquote>
  </blockquote>
  
  <p>On my last project, with the same package.json i don't have any error.
  Have you a solution ?</p>
  
  <p>Thank you</p>