[webauthn] new commits pushed by vijaybh

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

* Updates to reflect publication of WD-04

Minor editorial changes to pass validation:

dfn of makeCredential in section headings was conflicting with the IDL
definition

setAttestationChallenge URL exposes issues in Bikeshed and Specberus:
- Bikeshed's link processing of the `[text](url)` construct breaks if
url has a closing parenthesis
- Specberus thinks [ and ] are invalid characters in URLs even though
they should be legal
  by Vijay Bharadwaj
https://github.com/w3c/webauthn/commit/ce7925cac738fea9a7d81405815aef07f8cc60f2