title: import bootstrap variables in my style.sass issue
body: <p>I am trying to import bootstrap 4 beta variables partial in my style.sass but when i compile i get the following error:</p>
  
  <blockquote>
    <p>events.js:160
          throw er; // Unhandled 'error' event
          ^ Error: node_modules\bootstrap\scss_variables.scss Error: argument <code>$color</code> of <code>darken($color, $amount)</code> must be a color</p>
  
  <pre><code>   Backtrace:
      node_modules/bootstrap/scss/_variables.scss:168, in function `darken`
      node_modules/bootstrap/scss/_variables.scss:168
      on line 168 of node_modules/bootstrap/scss/_variables.scss
  </code></pre>
    
    <blockquote>
      <blockquote>
        <p>$link-hover-color:      darken($link-color, 15%) !default;    ------------------------^</p>
      </blockquote>
    </blockquote>
  
  <pre><code>at options.error (C:\Users\Giannis\Desktop\np-lab\node_modules\node-sass\lib\index.js:291:26)
  </code></pre>
  </blockquote>
  
  <p>here is my code:</p>
  
  <pre><code>@import "../../../node_modules/bootstrap/scss/variables"
  
  body
    background-color: red
  </code></pre>
  
  <p>Any ideas what is going on? 
  thanks</p>