When a tag exists, it silently fails

[bkielbasa]

Hi!

I noticed that when I try to create a new release that already exists, it fails without any information on what went wrong. I think it's because of those lines https://github.com/opspec-pkgs/github.release.create/blob/master/cmd.sh#L24
It would be very helpful to know what went wrong in a case of error.