title: `requestAnimationFrame` polyfill error in Jest tests
body: <p>Got this error after upgrading to React when I ran my Jest unit tests:</p>
  
  <pre><code>React depends on requestAnimationFrame. Make sure that you load a polyfill in older browsers.
  </code></pre>
  
  <p>How do I fix it?</p>
  
  <p>I'm using Jest 18.1.0.</p>