title: React-router error: super expression must either be null or a function
body: <p>I am new to react-router (<a href="https://github.com/rackt/react-router">https://github.com/rackt/react-router</a>). I included it after react like this:</p>
  
  <pre><code>&lt;script src="http://fb.me/react-0.12.2.js"&gt;&lt;/script&gt;
  &lt;script src="https://cdnjs.cloudflare.com/ajax/libs/reactrouter/0.13.2/ReactRouter.js"&gt;&lt;/script&gt;
  </code></pre>
  
  <p>I got an error:
  Uncaught TypeError: Super expression must either be null or a function, not undefined</p>
  
  <p>What did I do wrong?</p>