title: Mentions with a Custom Build
body: <p>I have a custom CKEditor 5 build (which includes the Mention plugin). The Custom editor loads and works great. But I cannot get the mention plugin to work. The '@' symbol does not trigger the autocomplete. If I enable the plugins line of the config the editor will not load.</p>
  <p>I am using anulgar.</p>
  <pre><code>import * as CustomEditor from '../libs/ckeditor5-build-custom/build/ckeditor';
  import Mention from '../libs/ckeditor5-build-custom/build/ckeditor';
  
  ...
  
   editorConfig = {
      //plugins : [Mention],
      mention: {
          feeds: [
              {
                  marker: '@',
                  feed: ['@Barney', '@Lily', '@Marshall', '@Robin', '@Ted'],
                  minimumCharacters: 1
              }
          ]
      }
  </code></pre>