ssh-copy-id version 6.4p1

This follows the OpenSSH Formula update to the same. 

Unfortunately I don't think it would be easy to refer to the OpenSSH Formula directly as that's in the dupes repo and not here.

Also - re testing - it doesn't look like this binary can be easily tested. It would need to actually install a key somewhere to do so. The help flags (-h and -?) return 1 for the exit code (error), so even a 'successful' `brew test` run comes back as as an error. Bummer.