[w3c/webauthn] 662a77: Add reference for U2F message formats

  Branch: refs/heads/vgb-u2f-attestation
  Home:   https://github.com/w3c/webauthn
  Commit: 662a775443c87c060e528d71e81dae91068f7a7b
      https://github.com/w3c/webauthn/commit/662a775443c87c060e528d71e81dae91068f7a7b
  Author: Vijay Bharadwaj <vijaybh@users.noreply.github.com>
  Date:   2017-01-11 (Wed, 11 Jan 2017)

  Changed paths:
    M index.bs

  Log Message:
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  Add reference for U2F message formats