title: Slim v3 duplicates cache-control header
body: <p>I have to return a specific cache-control header (<code>Cache-Control: public, max-stale=13910400</code>) but when run this, I get this: <a href="https://i.stack.imgur.com/KuyCU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/KuyCU.png" alt="Curl -v"></a></p>
  
  <p>Cache-control has been duplicated, but I only need custom values.</p>
  
  <pre><code>$newResponse = $response-&gt;withHeader('Cache-Control', 'public, max-stale=13910400')-&gt;withJson($appInfo);
  return $newResponse;
  </code></pre>
  
  <p>I tried this but it doesn't work (just for testing):</p>
  
  <pre><code>$newResponse = $response-&gt;withoutHeader('Cache-Control')-&gt;withHeader('Cache-Control', 'public, max-stale=13910400')-&gt;withJson($appInfo);
  return $newResponse;
  </code></pre>
  
  <p>How can I set the header correctly? </p>
  
  <p>Thank you</p>