title: angular6 - ngx-editor icons do not appear on production
body: <p>I am developing an angular6 app.
  I am using ngx-editor.</p>
  
  <p>The editor seems to work fine in localhost, but when I deploy it in firebase the icons don't appear at all.</p>
  
  <p><a href="https://i.stack.imgur.com/2Jjb8.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2Jjb8.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/nTyj9.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nTyj9.png" alt="enter image description here"></a></p>
  
  <p>What could be the reason? 
  Please let me know if you need any more details.</p>
  
  <p>TIA.</p>