doc: fix typo in zlib.md

PR-URL: https://github.com/nodejs/node/pull/32901


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Zeyu Yang <himself65@outlook.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>