Revert `gh` to `hub`

`hub`, like `gh`, is now powered by `go`.

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.
Should we wait until it's out of preview before making this change?

What is going to happen to `gh`?