title: How to group buttons in datatables with export buttons?
body: <p>I have a dropdown button with all export buttons coming inside its dropdown and outside I have two more buttons which are not grouping up with Export dropdown button.</p>
  
  <pre class="lang-js prettyprint-override"><code>buttons: [{
    extend: 'collection',
    text: 'Export',
    className: 'btn btn-sm btn-outline-dark',
    buttons: [{
      extend: 'excel',
      title: 'Re-assigned-Queries'
    }, {
      extend: 'pdf',
      title: 'Re-assigned-Queries'
    }, {
      extend: 'csv',
      title: 'Re-assigned-Queries'
    }]
  }, {
    text: 'Select all',
    className: 'btn btn-sm btn-outline-blue',
    action: function() {
      reassignQueryTable.rows().select();
    }
  }, {
    text: 'Select none',
    className: 'btn btn-sm btn-outline-red',
    action: function() {
      reassignQueryTable.rows().deselect();
    }
  }],
  </code></pre>
  
  <p>Export button is coming separated from other two buttons and the other two buttons are coming as grouped.
  I want all the 3 buttons to be grouped in one.</p>
  
  <p><a href="https://i.stack.imgur.com/NJ7mM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NJ7mM.png" alt="enter image description here"></a></p>