[webauthn] new commits pushed by christiaanbrand

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

* Clarifying signing procedure for U2F attestation

This closes #530
  by balfanz
https://github.com/w3c/webauthn/commit/5502d42d31d1aa5b6bc79f686cfecf0c6dbf04f5

* Merge pull request #571 from w3c/balfanz-patch-2

Clarifying signing procedure for U2F attestation
  by Christiaan Brand
https://github.com/w3c/webauthn/commit/96b9a982b235144816abaaa6517d364eef8dd824