doc: fix actual result of example is different in events

Refs: nodejs#50428

Author: deokjinkim

doc/api/events.md

@@ -73,6 +73,7 @@ myEmitter.on('event', function(a, b) {
   //     _events: [Object: null prototype] { event: [Function (anonymous)] },
   //     _eventsCount: 1,
   //     _maxListeners: undefined,
+  //     [Symbol(shapeMode)]: false,
   //     [Symbol(kCapture)]: false
   //   } true
 });
@@ -90,6 +91,7 @@ myEmitter.on('event', function(a, b) {
   //     _events: [Object: null prototype] { event: [Function (anonymous)] },
   //     _eventsCount: 1,
   //     _maxListeners: undefined,
+  //     [Symbol(shapeMode)]: false,
   //     [Symbol(kCapture)]: false
   //   } true
 });