title: Can't add custom fonts to CKEditor 4
body: <p>i know this question is probably asked alot ald, and i ald found many people asking this question. But somehow i still couldnt figure out for this to work. Im trying to add new custom fonts to my CKeditor for my MVC5 application. About a week ago, i added new fonts via config.js n it worked fine. But now, it just doesnt work anymore, it keeps showing my old fonts that i added from a week ago. I tried reinstall Ckeditor into my solution, clear my browser cache...etc. Also, i found out that even tho i remove ckeditor package from the solution, when i run the application, i can still use ckeditor so i think this might be a reason.
  Here're my code:</p>
  
  <h2>config.js</h2>
  
  <pre><code>/**
       * @license Copyright (c) 2003-2018, CKSource - Frederico Knabben. All rights reserved.
       * For licensing, see https://ckeditor.com/legal/ckeditor-oss-license
       */
  
      CKEDITOR.editorConfig = function( config ) {
          config.contentsCss = 'fonts.css'
          config.font_names = 'Khmer_OS;'
      };
  </code></pre>
  
  <h2>fonts.css :</h2>
  
  <pre><code>@font-face {
      font-family: "Khmer_OS";
      src: local("Khmer_OS"), url("fonts/KHMEROS.TTF") format('opentype'); /*non-IE*/
  }
  </code></pre>