hub: Update net/hub to 2.4.0

Changes:
2.4.0
-----
### Features
* `hub delete [<OWNER>/]<REPO>`
* Add `hub compare --copy` flag
* Add `hub release --format=<FORMAT>` option
* Add `hub pull-request --no-edit` flag
* When checking out a pull request, ensure that `git push`with no arguments
  works
* Support XDG Base Directory Specification

### Tweaks
* Enable `hub pr list -h <BRANCH>` when owner isn't specified
* Include `docs/` in list of locations to look up pull request and issue
  templates in

(leot)