meta: fix collaborator list errors in README.md

Add missing `-` characters in the list.

PR-URL: https://github.com/nodejs/node/pull/31655


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Yuta Hiroto <hello@hiroppy.me>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>