meta: update collaborator email in README

Update email for Shelley Vohr to correspond to what is specified in
.mailmap and what is used in more recently authored commits.

PR-URL: https://github.com/nodejs/node/pull/39521


Reviewed-By: Zeyu Yang <himself65@outlook.com>
Reviewed-By: Ujjwal Sharma <ryzokuken@disroot.org>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>