Layout: Adjust placement of ganalytics js

The instructions from google are not clear and error-prone. Place the js within
the head, at the end, not after the head.

References #355

app/views/layouts/application.html.haml

@@ -17,13 +17,12 @@
     = stylesheet_link_tag 'application', media: 'all', 'data-turbolinks-track': 'reload'
     = javascript_include_tag 'application', 'data-turbolinks-track': 'reload'
     = javascript_importmap_tags
-  / Google tag (gtag.js) should be after head.
-  %script{ src: "https://www.googletagmanager.com/gtag/js?id=G-PTHXK9D0S0"}
-  :javascript
-    window.dataLayer = window.dataLayer || [];
-    function gtag(){dataLayer.push(arguments);}
-    gtag('js', new Date());
-    gtag('config', 'G-PTHXK9D0S0');
+    %script{ src: "https://www.googletagmanager.com/gtag/js?id=G-PTHXK9D0S0"}
+    :javascript
+      window.dataLayer = window.dataLayer || [];
+      function gtag(){dataLayer.push(arguments);}
+      gtag('js', new Date());
+      gtag('config', 'G-PTHXK9D0S0');
   %body{class: "#{controller.action_name}"}
     = include_gon(:init => true)
     = render 'layouts/nav'