title: GCM click_action property on payload is not appearing
body: <p>I'm trying to use the click_action property on iOS which is like category for them, but the payload doesn't send the click_action option inside. and really weird</p>
  
  <pre><code>$payLoad['notification'] = [
              'title' =&gt; $push-&gt;getTitle(),
              'text'  =&gt; $push-&gt;getAlert(),
              'badge' =&gt; 1,
              'sound' =&gt; 'default',
              'click_action' =&gt; $push-&gt;getClickAction()
          ];
  </code></pre>
  
  <p>Is there something about it? or maybe if will be an option to send it in the custom-data?</p>