Log Message:
hub: Update net/hub to 2.5.1

Changes:
2.5.1
-----
* `hub issue create`: ignore the `.github/ISSUE_TEMPLATE` directory instead of
  crashing
* `hub pull-request`: avoid re-requesting reviewers in case of CODEOWNERS
* `hub ci-status`: handle cases when Checks API is unavailable, like older
  GitHub Enterprise
* Handle HTTP 422 message format from server response
* Ignore crash for malformed `~/.config/hub` file
* Clarify `hub init -g` documentation that it doesn't imply `hub create`
* `hub clone`: add more documentation about git protocol used