Migrate to gtag.js

index.html

@@ -4,6 +4,15 @@
   <meta charset="utf-8">
   <title>2048</title>
 
+  <script async src="https://www.googletagmanager.com/gtag/js?id=UA-42620757-2"></script>
+  <script>
+    window.dataLayer = window.dataLayer || [];
+    function gtag(){dataLayer.push(arguments);}
+    gtag("js", new Date());
+
+    gtag("config", "UA-42620757-2");
+  </script>
+
   <link href="style/main.css" rel="stylesheet" type="text/css">
   <link rel="shortcut icon" href="favicon.ico">
   <link rel="apple-touch-icon" href="meta/apple-touch-icon.png">
@@ -171,15 +180,5 @@
   <script src="js/local_storage_manager.js"></script>
   <script src="js/game_manager.js"></script>
   <script src="js/application.js"></script>
-
-  <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");
-
-    ga("create", "UA-42620757-2", "gabrielecirulli.github.io");
-    ga("send", "pageview");
-  </script>
 </body>
 </html>