[w3c/webauthn] d448eb: Don't say user handle is optional in Public Key Cr...

  Branch: refs/heads/issue-720-user-handle-optional
  Home:   https://github.com/w3c/webauthn
  Commit: d448eb3a2da0b5682cdf98c10c6a3ee5d399d667
      https://github.com/w3c/webauthn/commit/d448eb3a2da0b5682cdf98c10c6a3ee5d399d667
  Author: Emil Lundberg <emil@yubico.com>
  Date:   2017-12-08 (Fri, 08 Dec 2017)

  Changed paths:
    M index.bs

  Log Message:
  -----------
  Don't say user handle is optional in Public Key Credential Source definition

This resolves #720.