Remove homebrew warning 'brew upgrade --cleanup' is deprecated!'
Remove homebrew warning 'brew upgrade --cleanup' is deprecated!'

Remove this warning with homebrew 1.9:

  Warning: Calling 'brew upgrade --cleanup' is deprecated! Use 'HOMEBREW_INSTALL_CLEANUP' instead.

See https://brew.sh/2019/01/09/homebrew-1.9.0/:
  brew upgrade --cleanup and HOMEBREW_UPGRADE_CLEANUP have been replaced with the HOMEBREW_INSTALL_CLEANUP variable. These will become default behaviours in 2.0.0.

nicokosi/dotfiles,nicokosi/dotfiles