chore: change from handlebars to html comment

Co-authored-by: Chris Manson <[email protected]>

Author: matthewhartstonge

tests/dummy/app/index.html

@@ -25,7 +25,7 @@
 
     {{content-for "body-footer"}}
 
-    {{!-- Place this tag in your head or just before your close body tag. --}}
+    <!-- Place this tag in your head or just before your close body tag. -->
     <script async defer src="https://buttons.github.io/buttons.js"></script>
   </body>
 </html>