title: What's the ruby syntax headers "Access-Control-Allow-Headers" => "x-requested-with"?
body: <p>I think it's pass a hash to the headers method,</p>
  
  <p>But I don't know why </p>
  
  <pre><code>headers {"Access-Control-Allow-Headers" =&gt; "x-requested-with"}
  </code></pre>
  
  <p>doesn't work.</p>