title: Sass Breakpoint won't work - what am I doing wrong?
body: <p>I just installed Breakpoint, added </p>
  
  <pre><code>require "breakpoint"
  </code></pre>
  
  <p>to my config.rb, and defined these breakpoints</p>
  
  <pre><code>$mobileMedium : 480px;
  $tabletVertical : 768px;
  $desktopNormal : 1024px;
  $desktopWide : 1200px;
  </code></pre>
  
  <p>to my _breakpoint.scss.</p>
  
  <p>When I tried to use one of the breakpoints, like this;</p>
  
  <pre><code>@include breakpoint($mobileMedium) {
  …
  }
  </code></pre>
  
  <p>terminal told me</p>
  
  <pre><code>error sass/screen.scss (Line 27: Undefined mixin 'breakpoint'.)
  </code></pre>
  
  <p>why is that?</p>