add a check for production (#1335)

layouts/partials/hooks/body-end.html

@@ -1,4 +1,6 @@
 {{/* Use this file to include anything you wish to append to the end of the body tag */ -}}
 <!-- GTM code snippet for js disabled browsers -->
  <!-- Placing the noscript code snippet at the end of the body can lead to missing some events during page load, but since users with JavaScript disabled browsers are rare, this placement is acceptable. -->
+{{ if hugo.IsProduction -}}
     {{ partial "gtm-noscript.html" . }}
+{{ end -}}

layouts/partials/hooks/head-end.html

@@ -1,3 +1,5 @@
 {{ partial "meta.html" . -}}
 {{ partial "favicons.html" . -}}
+{{ if hugo.IsProduction -}}
     {{ partial "gtm.html" . }}
+{{ end -}}