title: how to change class of a label for checkboxes in simple_form
body: <p>using <code>simple_form</code> we can change class of a label using:</p>
  
  <p><code>label_html =&gt; {:class =&gt; "myclass"}</code></p>
  
  <p>but how do we do the same when dealing with checkboxes?</p>
  
  <p><code>simple_form</code> assigns the default class of <code>collection_check_boxes</code> </p>
  
  <p>Is there a way to change this default class?</p>