Update .mailmap

Author: JohnTitor

.mailmap

@@ -263,6 +263,7 @@ Xuefeng Wu <benewu@gmail.com> Xuefeng Wu <xfwu@thoughtworks.com>
 Xuefeng Wu <benewu@gmail.com> XuefengWu <benewu@gmail.com>
 York Xiang <bombless@126.com>
 Youngsoo Son <ysson83@gmail.com> <ysoo.son@samsung.com>
+Yuki Okushi <huyuumi.dev@gmail.com>
 Zach Pomerantz <zmp@umich.edu>
 Zack Corr <zack@z0w0.me> <zackcorr95@gmail.com>
 Zack Slayton <zack.slayton@gmail.com>