mailmap: add entry for myself

Signed-off-by: Linjie Fu <linjie.justin.fu@gmail.com>

.mailmap

@@ -10,7 +10,8 @@
 <barryjzhao@tencent.com> <jun.zhao@intel.com>
 <josh@itanimul.li> <joshdk@obe.tv>
 <michael@niedermayer.cc> <michaelni@gmx.at>
-<linjie.fu@intel.com> <fulinjie@zju.edu.cn>
+<linjie.justin.fu@gmail.com> <linjie.fu@intel.com>
+<linjie.justin.fu@gmail.com> <fulinjie@zju.edu.cn>
 <ceffmpeg@gmail.com> <cehoyos@ag.or.at>
 <ceffmpeg@gmail.com> <cehoyos@rainbow.studorg.tuwien.ac.at>
 <ffmpeg@gyani.pro> <gyandoshi@gmail.com>