Maintainers.txt: Update Liming mail address

Signed-off-by: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Andrew Fish <afish@apple.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Message-Id: <20200821144949.654-1-gaoliming@byosoft.com.cn>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>