Updating pointer to new _project.yaml file from internal changelist 461499214. (#6451)

Author: egilmorez

scripts/docgen-compat/theme/layouts/default.hbs

@@ -4,7 +4,7 @@
     <meta charset="utf-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="project_path" value="/docs/reference/js/_project.yaml" />
     <meta name="book_path" value="/docs/reference/_book.yaml" />
     <meta name="translation" value="disabled" />
     <meta name="page_type" value="reference" />