GitHub command-line client Formula was removed
Last versions were
gh requires the following formula to be installed:
go 1.9.2 Open source programming language to build simple/reliable/efficient software

Formula history

ilovezfs gh: delete (#16903)
Dominyk Tiller gh: don't lean on HOMEBREW_REPOSITORY
Tomasz Pajor gh: audit fixes
Nikolaus Wittenstein Add descriptions to all remaining homebrew packages
Mike McQuaid gh: mark bottle as relocatable.
Mike McQuaid gh: fix strict audit failures.
Mike McQuaid gh: add Yosemite bottle.
Jack Nagel gh: install man page
Jingwen Owen Ou gh 2.1.0 (new formula) - GitHub CLI.