doc: fix actual result of example is different in events
Change of events internal may be not reflected yet.
In document, result of example is like below.
a b MyEmitter {
domain: null,
_events: { event: [Function] },
_eventsCount: 1,
_maxListeners: undefined } true
But actual result of example with current node is like below.
a b MyEmitter {
_events: [Object: null prototype] { event: [Function (anonymous)] },
_eventsCount: 1,
_maxListeners: undefined,
[Symbol(kCapture)]: false
} true