erofs-utils: update my email address in README/AUTHORS

My previous email address was no longer valid. Fix it.

Link: https://lore.kernel.org/r/20210102052055.3734591-1-hsiangkao@redhat.com
Reported-by: Hu Weiwen <huww98@outlook.com>
Signed-off-by: Gao Xiang <hsiangkao@aol.com>