doc: update collaborator email address

Per email conversation with Shigeki Ohtsu, updating email address in
docs. The current listed email address does not work anymore.

PR-URL: https://github.com/nodejs/node/pull/11996
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Shigeki Ohtsu <ohtsu@ohtsu.org>

.mailmap

@@ -143,7 +143,7 @@ San-Tai Hsu <v@fatpipi.com>
 Scott Blomquist <github@scott.blomqui.st> <sblom@microsoft.com>
 Sergey Kryzhanovsky <skryzhanovsky@gmail.com> <another@dhcp199-223-red.yandex.net>
 Shannen Saez <shannenlaptop@gmail.com>
-Shigeki Ohtsu <ohtsu@d.jp> <ohtsu@iij.ad.jp>
+Shigeki Ohtsu <ohtsu@d.jp> <ohtsu@iij.ad.jp> <ohtsu@ohtsu.org>
 Siddharth Mahendraker <siddharth_mahen@hotmail.com> <siddharth_mahen@me.com>
 Simon Willison <simon@simonwillison.net>
 Stanislav Opichal <opichals@gmail.com>

README.md

@@ -185,7 +185,7 @@ more information about the governance of the Node.js project, see
 * [rvagg](https://github.com/rvagg) -
 **Rod Vagg** <rod@vagg.org>
 * [shigeki](https://github.com/shigeki) -
-**Shigeki Ohtsu** <ohtsu@iij.ad.jp> (he/him)
+**Shigeki Ohtsu** <ohtsu@ohtsu.org> (he/him)
 * [targos](https://github.com/targos) -
 **Michaël Zasso** <targos@protonmail.com> (he/him)
 * [thefourtheye](https://github.com/thefourtheye) -