[w3c/webauthn] 95fd62: Fix User.ID example

  Branch: refs/heads/christiaanbrand-patch-1
  Home:   https://github.com/w3c/webauthn
  Commit: 95fd62a3844a95c6cd9065fee90d73e60583f3fc
      https://github.com/w3c/webauthn/commit/95fd62a3844a95c6cd9065fee90d73e60583f3fc
  Author: Christiaan Brand <christiaan@entersekt.com>
  Date:   2017-10-11 (Wed, 11 Oct 2017)

  Changed paths:
    M index.bs

  Log Message:
  -----------
  Fix User.ID example

Make User.ID binary in example 2 in section 11. Closes #598