zsh completions have been installed to:
  /usr/local/share/zsh/site-functions

$ ls  /usr/local/share/zsh/site-functions
_aws                    _brew_cask              _gibo                   _heroku                 aws_zsh_completer.sh
_brew                   _brew_services          _git                    _kubectl                git-completion.bash

fpath=(/usr/local/share/zsh/site-functions $fpath)

autoload -U compinit
compinit