[Node] Fixing WritableStream.write and WritableStream.end.

Documentation for WritableStream.write:
http://nodejs.org/api/stream.html#stream_writable_write_chunk_encoding_callback

There's no 'fd' argument; that might have been a typo.

You can call `write` in the following ways:
* `write(data: Buffer)`
* `write(data: Buffer, cb: Function)`
* `write(data: String)`
* `write(data: String, cb: Function)`
* `write(data: String, encoding: String)`
* `write(data: String, encoding: String, cb: Function)`

The same goes to `end`, except `end` can be called with no arguments, too.