.mailmap: map Yi-Jyun Pan's email

In 13185fd241 (l10n: zh_TW.po: update translation for v2.25.0 round 1,
2019-12-31), the author mistakenly used their GitHub username for
authorship information instead of their real name. However, a commit
with their real name exists prior to this: 9917eca794 (l10n: zh_TW: add
translation for v2.24.0, 2019-11-20).

Map their email to their real name so that these contributions can be
counted together.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.mailmap

@@ -288,6 +288,7 @@ William Pursell <bill.pursell@gmail.com>
 YONETANI Tomokazu <y0n3t4n1@gmail.com> <qhwt+git@les.ath.cx>
 YONETANI Tomokazu <y0n3t4n1@gmail.com> <y0netan1@dragonflybsd.org>
 YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
+Yi-Jyun Pan <pan93412@gmail.com>
 # the two anonymous contributors are different persons:
 anonymous <linux@horizon.com>
 anonymous <linux@horizon.net>