doc: fix module.children description

Updates the module.children description in the docs to match current
functionality in that it will only contain the modules required for the
first time by this module.

Fixes: #9371

PR-URL: #21672
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/modules.md

@@ -693,7 +693,7 @@ added: v0.1.16
 
 * {module[]}
 
-The module objects required by this one.
+The module objects required for the first time by this one.
 
 ### module.exports
 <!-- YAML