doc: fix a typo in util.isDeepStrictEqual

Backport-PR-URL: https://github.com/nodejs/node/pull/19127
PR-URL: https://github.com/nodejs/node/pull/18775


Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>