doc: update changelog for io.js v3.2.0

Notable changes:

* events: Added EventEmitter#listenerCount(event) as a replacement for
  EventEmitter.listenerCount(emitter, event), which has now been
  marked as deprecated in the docs. (Sakthipriyan Vairamani) #2349
* module: Fixed an error with preloaded modules when the current
  working directory doesn't exist. (Bradley Meck) #2353
* node: Startup time is now about 5% faster when not passing V8 flags.
  (Evan Lucas) #2483
* repl: Tab-completion now works better with arrays.
  (James M Snell) #2409
* string_bytes: Fixed an unaligned write in the handling of UCS2
  encoding. (Fedor Indutny) #2480
* tls: Added a new --tls-cipher-list flag that can be used to override
  the built-in default cipher list. (James M Snell) #2412

PR-URL: https://github.com/nodejs/node/pull/2512