data8/_includes/google_analytics.html

{% if site.google_analytics.mytrackingcode %}
<!-- Global site tag (gtag.js) - Google Analytics -->
<script async src="https://www.googletagmanager.com/gtag/js?id={{ site.google_analytics.mytrackingcode }}"></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());

  gtag('config', '{{ site.google_analytics.mytrackingcode }}');
</script>
{% endif %}