(pwa): preload GA script

Author: Pablo Vieira

_includes/analytics.html

@@ -1,14 +1,11 @@
 {% if site.ga_tracking_code %}
   <!-- Google Analytics -->
   <script>
-    (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
-    (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
-    m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
-    })(window,document,'script','//www.google-analytics.com/analytics.js','ga');
-
+    window.ga=window.ga||function(){(ga.q=ga.q||[]).push(arguments)};ga.l=+new Date;
     ga('create', '{{ site.ga_tracking_code }}', 'auto');
     ga('send', 'pageview');
   </script>
+  <script async src='https://www.google-analytics.com/analytics.js'></script>
   <!-- Google Analytics end -->
 {% endif %}