Update to 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
    
    Signed-off-by: Stephen Gallagher <sgallagh@redhat.com>