tools: use long format for gpg fingerprint

Git has been using my Long format fingerprint in the tagging messages,
this has been causing the release script to fail on my keys.

It would also be wise to be using the long format on keys based on some
attacks that hack been found in the wild around short keys.

PR-URL: https://github.com/nodejs/node/pull/9258


Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>