Add self to mailmap.

Author: jumbatm

.mailmap

@@ -139,6 +139,7 @@ Jorge Aparicio <japaric@linux.com> <japaricious@gmail.com>
 Joseph Martin <pythoner6@gmail.com>
 Joseph T. Lyons <JosephTLyons@gmail.com> <josephtlyons@gmail.com>
 Joseph T. Lyons <JosephTLyons@gmail.com> <JosephTLyons@users.noreply.github.com>
+jumbatm <jumbatm@gmail.com> <30644300+jumbatm@users.noreply.github.com>
 Junyoung Cho <june0.cho@samsung.com>
 Jyun-Yan You <jyyou.tw@gmail.com> <jyyou@cs.nctu.edu.tw>
 Kang Seonghoon <kang.seonghoon@mearie.org> <public+git@mearie.org>