Revert gh to hub

`hub`, like `gh`, is now powered by the Go programming language.

https://github.com/github/hub#2x

Since `gh` is a GitHub CLI,
why not use the CLI created by GitHub themselves?

Additionally, `hub` handles `$ git clone thoughtbot/laptop`
out of the box.

`hub` 2.2.0 is the first stable release using Go:

https://github.com/github/hub/releases/tag/v2.2.0

It has been bottled in Homebrew:

Homebrew/legacy-homebrew@1ad37e4

mac

@@ -143,7 +143,7 @@ brew_install_or_upgrade 'tmux'
 brew_install_or_upgrade 'reattach-to-user-namespace'
 brew_install_or_upgrade 'imagemagick'
 brew_install_or_upgrade 'qt'
-brew_install_or_upgrade 'gh'
+brew_install_or_upgrade 'hub'
 brew_install_or_upgrade 'node'
 
 brew_install_or_upgrade 'rbenv'