Fixing the book path meta tag on generated docs (#558)

* Fixing the book path meta tag on generated docs

* Fixed typo

Author: hiranya911

docgen/content-sources/node/HOME.md

@@ -6,4 +6,4 @@ You can install it via our [npm package](https://www.npmjs.com/package/firebase-
 To get started using the Firebase Admin Node.js SDK, see
 [Add the Firebase Admin SDK to your server](https://firebase.google.com/docs/admin/setup).
 
-For source code, see the [Firebase Admin Node.js SDK Github repo](https://github.com/firebase/firebase-admin-node).
+For source code, see the [Firebase Admin Node.js SDK GitHub repo](https://github.com/firebase/firebase-admin-node).

docgen/theme/layouts/default.hbs

@@ -5,7 +5,8 @@
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <meta name="hide_page_heading" value="true" />
     <meta name="project_path" value="/_project.yaml" />
-    <meta name="book_path" value="/_book.yaml" />
+    <meta name="book_path" value="/docs/reference/_book.yaml" />
+    <meta name="gtm_var" data-key="docType" data-value="reference">
     <title>{{#ifCond model.name '==' project.name}}{{project.name}}{{else}}{{model.name}} | {{project.name}}{{/ifCond}}</title>
     <meta name="description" content="Reference for {{model.name}}">
     <meta name="viewport" content="width=device-width, initial-scale=1">
@@ -29,4 +30,4 @@
 {{> analytics}}
 
 </body>
-</html>
+</html>