title: tinymce keyup event doesn't fire on tab key
body: <p>I am using tinymce 4.3.2 and I am trying to add a custom event when you press the tab key inside the editor. 
  Here's my setup using the jquery plugin:</p>
  
  <pre><code>$(el).tinymce({
      theme: "modern",
      plugins: [
          'textcolor'
      ],
      toolbar: 'bold italic underline forecolor',
      menubar: false,
      statusbar: false,
      setup: function(editor) {
          editor.on('keyup', function(e) {
              console.log('keyup event fired');
          });
      }
  });
  </code></pre>
  
  <p>However, when I press the tab key, this keyup function does not seem to run.</p>