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 <info@bnoordhuis.nl>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

lib/fs.js

@@ -1895,8 +1895,11 @@ util.inherits(SyncWriteStream, Stream);
 
 
 // Export
-fs.SyncWriteStream = SyncWriteStream;
-
+Object.defineProperty(fs, 'SyncWriteStream', {
+    configurable: true,
+    writable: true,
+    value: SyncWriteStream
+});
 
 SyncWriteStream.prototype.write = function(data, arg1, arg2) {
   var encoding, cb;