should reference "attestation statement format" registry instead of "extensions" registry

[equalsJeffH]

at the end of section 8.1. Attestation Statement Format Identifiers, we say:

The up-to-date list of registered WebAuthn Extensions is maintained in the IANA "WebAuthn Attestation Statement Format Identifiers" registry ...

which, in this section on extensions, ought to say:

The up-to-date list of registered WebAuthn Attestation Statement Format Identifiers is maintained in the IANA "WebAuthn Attestation Statement Format Identifiers" registry ...