you don't need hub to update pull requests. Pull requests are tied to the remote branch they're opened from (the pull-request "head"). Just push to that branch again and GitHub will automatically figure it out. You can even force-push, of you need that.
What if you accidentally have removed the remote branch that is linked to the PR? Is it possible to fetch the PR and link it to a new remote on your fork, so the PR can be updated? Asking for a friend...
So to update a PR, even if you have removed the original remote branch out of which the PR was created, you just need to:
- Fetch the PR (git fetch pull//head:branchname and git checkout branchname).
- Add new commits, amend, rebase, do whatever you like.
- Push or push force (git push remote +branch).
And after that the PR will be automagically updated :)