Switch from `hub` to `gh`

[gh] is a [hub] reimplementation that's much faster and is now the official
Github CLI. It appears that "hub" is [deprecated].

[gh]: https://github.com/jingweno/gh
[hub]: https://github.com/github/hub
[deprecated]: https://github.com/github/hub/issues/475
I assume `sudo dpkg -i foo.deb` is installing the package globally, as if it had come from the repos. I also assume such an installation puts the binary in the usual place. So I'm confused why the next line (`chmod +x ~/.bin/gh`) is happening.