doc: remove usage of events.EventEmitter

The `events` module already exports `EventEmitter` constructor function
So, we don't have to use `events.EventEmitter` to access it.

Refer: https://github.com/nodejs/node/pull/2896

PR-URL: https://github.com/nodejs/node/pull/2921


Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>