title: Callback action is not firing for columnsToggle button
body: <p>In the following <a href="https://jsfiddle.net/asanchez4096/urd5gquc/" rel="nofollow">JSFiddle</a> the action function does not fire whenever a button to select a column in the column visibility button is selected. Below is the code that I am using: </p>
  
  <pre><code>$(document).ready(function() {
  var table = $('#example').DataTable( {
      dom: 'B',
      "buttons": [
                  {
                      extend: 'colvis',
                      postfixButtons: ['colvisRestore'],
                      buttons : [{
                          extend: 'columnsToggle',
                          action: function (e, dt, node, config) {
                              alert('Activated!');
                              console.log("Activated!");
                          },
                      }],
                  }
              ],
      }
  );} );
  </code></pre>
  
  <p>I would really appreciate your help on this one.</p>