dev-vcs/hub: Hub has moved from defunkt to github

$ wget -S https://github.com/defunkt/hub
    --2013-08-06 13:37:14--  https://github.com/defunkt/hub
    Resolving github.com... 204.232.175.90
    Connecting to github.com|204.232.175.90|:443... connected.
    HTTP request sent, awaiting response...
      HTTP/1.1 301 Moved Permanently
      ...
      Status: 301 Moved Permanently
      ...
      Location: https://github.com/github/hub

The download still works with the old URL (after a few redirects), but
the filenames in the tarball have changed, so we need to update the
manifest anyway.

I also added `dev-lang/ruby` to hub's `RDEPEND`.