doc: avoid incomplete sentence in cluster docs

PR-URL: https://github.com/nodejs/node/pull/41701
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Mestery <mestery@protonmail.com>
Reviewed-By: Mohammed Keyvanzadeh <mohammadkeyvanzade94@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Harshitha K P <harshitha014@gmail.com>

doc/api/cluster.md

@@ -1062,7 +1062,7 @@ added: v0.7.0
 
 * {Object}
 
-A hash that stores the active worker objects, keyed by `id` field. Makes it
+A hash that stores the active worker objects, keyed by `id` field. This makes it
 easy to loop through all the workers. It is only available in the primary
 process.