certificate: fix bug in spki calculation
certificate: fix bug in spki calculation

mozilla/tls-observatory,jasonthomas/tls-observatory,jasonthomas/tls-observatory,mozilla/TLS-Observer,jasonthomas/tls-observatory,mozilla/tls-observatory,mozilla/tls-observatory,jasonthomas/tls-observatory,mozilla/tls-observatory,jasonthomas/tls-observatory,mozilla/tls-observatory