Use hidden

Author: reakaleek

docset.yml

@@ -40,7 +40,7 @@ toc:
   - toc: reference
   - toc: extend
   - toc: raw-migrated-files
-  - file: 404.md
+  - hidden: 404.md
 
 subs:
   ref:   "https://www.elastic.co/guide/en/elasticsearch/reference/current"