title: How can I get value of element custom attribute with Watir
body: <p>I have HTML that looks like this:</p>
  
  <pre><code>&lt;input custom_attribute="so cool" type="text" /&gt;
  </code></pre>
  
  <p>I would like to get value of <code>custom_attribute</code> using <a href="http://watir.com/" rel="nofollow noreferrer">Watir</a>.</p>