Use async Google Analytics tracking code

_layouts/default.html

@@ -48,14 +48,12 @@ <h1 class="header">{{ site.title | default: site.github.repository_name }}</h1>
     <!--[if !IE]><script>fixScale(document);</script><![endif]-->
     {% if site.google_analytics %}
       <script type="text/javascript">
-        var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www.");
-        document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));
-      </script>
-      <script type="text/javascript">
-        try {
-          var pageTracker = _gat._getTracker("{{ site.google_analytics }}");
-        pageTracker._trackPageview();
-        } catch(err) {}
+        (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');
+        ga('create', '{{ site.google_analytics }}', 'auto');
+        ga('send', 'pageview');
       </script>
     {% endif %}
   </body>