[webauthn] new commits pushed by jyasskin

The following commits were just pushed by jyasskin to https://github.com/w3c/webauthn:

* Rewrite Generating an Attestation Object as an algorithm. (#600)

This replaces the "first generate the authenticator data" step with an input
because that's how it's called.
  by Jeffrey Yasskin
https://github.com/w3c/webauthn/commit/8b23fb85f33c03e0420fb8182d9d774012546fd9