Update to 2.6.0
    
    https://github.com/github/hub/releases/tag/v2.6.0
    
    Features
      * Use "scissors" line to delineate comments in editable messages instead of
        stripping away lines that start with #
      * New command `hub issue show <NUMBER>`
      * Add `hub release show --format=<FORMAT>` functionality
      * `hub pr list --format=%rs` lists requested reviewers
      * Add support for communicating with GitHub Enterprise over Unix socket
    
    Fixes
      * Prevent `hub create` setting a public upstream when creating a private repo
      * Fix `hub release create/edit/delete` when there are multiple git remotes
      * Auto-detect private/pushable repos in `hub remote add`
      * Fix `hub ci-status` exit code when there is only Checks
      * Allow `hub compare <RANGE>` even if not on any branch
      * Ensure consistent sort direction when listing issues, PRs
      * Match requested team names by slug instead of name in
        `hub pull-request -r <TEAM>`
    
    Signed-off-by: Stephen Gallagher <sgallagh@redhat.com>