Google Analytics Universal Tracking Init in Google Tag Manager

gistfile1.js

<script>
  (function(q,u,i,c,k){window['GoogleAnalyticsObject']=q;
  window[q]=window[q]||function(){(window[q].q=window[q].q||[]).push(arguments)},
  window[q].l=1*new Date();c=i.createElement(u),k=i.getElementsByTagName(u)[0];
  c.async=true;c.src='//www.google-analytics.com/analytics.js';
  k.parentNode.insertBefore(c,k)})('ga','script',document);

  ga('create', 'UA-XXXXXXXX-XX', 'yourwebsite.com'); //make sure to customize your tracking ID and your domainname

  dataLayer.push({"event":"trackingLoaded"}); //don't forget to add this line

</script>