doc: fix: docstring: use Promise

frontend/static/js/api/matchmaking.js

@@ -19,7 +19,7 @@ class MatchMaking
 	 * @param {CallableFunction} receive_func 
 	 * @param {CallableFunction} disconnect_func 
 	 * @param {Number} mode The number of players in a game 
-	 * @returns {undefined}
+	 * @returns {Promise<?>}
 	 */
 	async start(receive_func, disconnect_func, mode)
 	{
@@ -50,6 +50,9 @@ class MatchMaking
 		this.disconnect_func(event);
 	}
 
+	/**
+	 * @returns {Promise<?>}
+	 */
 	async stop()
 	{
 		if (this._socket)