stream: update outdated highwatermark doc

PR-URL: nodejs#53494
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>

doc/api/stream.md

@@ -3428,7 +3428,7 @@ added:
 * Returns: {integer}
 
 Returns the default highWaterMark used by streams.
-Defaults to `16384` (16 KiB), or `16` for `objectMode`.
+Defaults to `65536` (64 KiB), or `16` for `objectMode`.
 
 ### `stream.setDefaultHighWaterMark(objectMode, value)`