DOP-1671: update GTM code (#507)

Author: Chris Cho

doc/_templates/layout.html

@@ -4,14 +4,14 @@
 
    {% if theme_googletag  %}
    <!-- Google Tag Manager -->
-      <noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-JQHP"
+      <noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-GDFN"
                        height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
       <script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push(
         {'gtm.start': new Date().getTime(),event:'gtm.js'}
       );var f=d.getElementsByTagName(s)[0],
       j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
       '//www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
-      })(window,document,'script','dataLayer','GTM-JQHP');</script>
+      })(window,document,'script','dataLayer','GTM-GDFN');</script>
       <!-- End Google Tag Manager -->
 
    {% endif %}