Add Gordon Chung to .mailmap
Add Gordon Chung to .mailmap

This dude uses two different names in the git log, confusing git-log and other
tools as there was two different authors.

leandroreox/gnocchi,gnocchixyz/gnocchi,sileht/gnocchi,leandroreox/gnocchi,gnocchixyz/gnocchi,sileht/gnocchi