Julian ending up solving it like this: https://github.com/coinbase/coinbase-ruby/commit/7bd9b6576bd267001202d21082a4c151fc87e4c4
He added some additional notes:
You can get the actual certificate chain from the authority in most cases: https://www.digicert.com/digicert-root-certificates.htm
Or something like this would also work:
openssl s_client -showcerts -connect yourwebsite.com:443