Fix instance exit notification

Fix improper notification on Factorio server exit causing plugins and
the instance tracking to fail.

lib/factorio/server.js

@@ -419,7 +419,7 @@ const outputHeuristics = [
  * output - invoked with parsed output from Factorio
  * rcon-ready - invoked when the RCON client has connected
  * game-ready - invoked when the server is finished starting up
- * stopped - invoked when the sterver has exited
+ * exit - invoked when the sterver has exited
  */
 class FactorioServer extends events.EventEmitter {
 	/**
@@ -636,7 +636,7 @@ class FactorioServer extends events.EventEmitter {
 			this._gameReady = false;
 			this._unexpected = [];
 
-			this.emit('stopped');
+			this.emit("exit");
 		});
 	}
 
@@ -678,6 +678,7 @@ class FactorioServer extends events.EventEmitter {
 		);
 
 		this._attachStdio();
+		this._server.once("exit", () => this.emit("exit"));
 
 		try {
 			let [code, signal] = await events.once(this._server, 'exit');