doc: fixed typo in n-api.md

PR-URL: https://github.com/nodejs/node/pull/38822


Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>