fs: make SyncWriteStream non-enumerable
fs: make SyncWriteStream non-enumerable

Make SyncWriteStream non-enumerable since it's only for internal use.

PR-URL: https://github.com/nodejs/io.js/pull/1870
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>
Reviewed-By: Trevor Norris <9cb5491eb5770dd8e0bf77a8a0335abf5f0488c5@gmail.com>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node