update proofreader
update proofreader

add Chinese Simplified(简体中文) proofreader @xiaogang_gitlab
stoplightio/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,iiet/iiet-git,mmkassem/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,stoplightio/gitlabhq,iiet/iiet-git,stoplightio/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq