MAINTAINERS: update Gyuho's contact email
Became independent contributor.
# MAINTAINERS
Brandon Philips <brandon@ifup.org> (@philips) pkg:*
-Gyuho Lee <gyuhox@gmail.com> <leegyuho@amazon.com> (@gyuho) pkg:*
+Gyuho Lee <gyuhox@gmail.com> (@gyuho) pkg:*
Hitoshi Mitake <h.mitake@gmail.com> (@mitake) pkg:*
Jingyi Hu <jingyih@google.com> (@jingyih) pkg:*
Joe Betz <jpbetz@google.com> (@jpbetz) pkg:*
