lib: change anonymous function to arrow function

PR-URL: https://github.com/nodejs/node/pull/24589


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Shingo Inoue <leko.noor@gmail.com>