doc: fix print results in events

PR-URL: nodejs#49548
Refs: nodejs#49537
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>

doc/api/events.md

@@ -105,7 +105,7 @@ class MyEmitter extends EventEmitter {}
 const myEmitter = new MyEmitter();
 myEmitter.on('event', (a, b) => {
   console.log(a, b, this);
-  // Prints: a b {}
+  // Prints: a b undefined
 });
 myEmitter.emit('event', 'a', 'b');
 ```