$ gem build wisper.gemspec
Enter PEM pass phrase:
INFO: Your certificate has expired, trying to re-sign it...
ERROR: While executing gem ... (Gem::Security::Exception)
certificate /CN=kris.leech\/DC=gmail\/DC=com not valid after 2020-10-15 18:13:45 UTC
$ gem cert --re-sign -C gem-public_cert.pem -K ~/.ssh/gem-private_key.pem