title: Upgraded Rails to 6, getting Blocked host Error
body: <p>I needed the new function in ActiveStorage to resize_to_fill so I upgraded to Ruby 2.5.1 and Rails 6.</p>
  <pre><code>ruby '2.5.1'
  
  gem &quot;rails&quot;, github: &quot;rails/rails&quot;
  </code></pre>
  <p>When I stopped, then restarted my server (Cloud 9), I received the below Rails error:</p>
  <pre><code>Blocked host: xxxxxxx-xxxxxxx.c9users.io
  To allow requests to xxxxxxx-xxxxxxx.c9users.io, add the following configuration:
  
  Rails.application.config.hosts &lt;&lt; &quot;xxxxxxx-xxxxxxx.c9users.io&quot;
  </code></pre>
  <p>I've tried restarting, new windows, but nothing worked. I've never seen this error before. I'm guessing the new version of Rails is doing something?</p>