Fix menu id in frontmatter

Author: tamalsaha

docs/standalone.md

@@ -3,7 +3,7 @@ title: PostgreSQL | Stash
 description: Backup and restore standalone PostgreSQL database using Stash
 menu:
   product_stash_{{ .version }}:
-    identifier: standalone-postgres
+    identifier: standalone-postgres-{{ .subproject_version }}
     name: Standalone PostgreSQL
     parent: stash-postgres-guides-{{ .subproject_version }}
     weight: 10