[w3c/webauthn] ce7925: Updates to reflect publication of WD-04

  Branch: refs/heads/master
  Home:   https://github.com/w3c/webauthn
  Commit: ce7925cac738fea9a7d81405815aef07f8cc60f2
      https://github.com/w3c/webauthn/commit/ce7925cac738fea9a7d81405815aef07f8cc60f2
  Author: Vijay Bharadwaj <vijaybh@users.noreply.github.com>
  Date:   2017-02-16 (Thu, 16 Feb 2017)

  Changed paths:
    M index.bs

  Log Message:
  -----------
  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