[w3c/webauthn] b0f283: Incorporate feedback from JeffH, part 3

  Branch: refs/heads/vgb-refine-makecredential
  Home:   https://github.com/w3c/webauthn
  Commit: b0f283e67f6bd77ffe177944c83b52c0c80b1d53
      https://github.com/w3c/webauthn/commit/b0f283e67f6bd77ffe177944c83b52c0c80b1d53
  Author: Vijay Bharadwaj <vijaybh@users.noreply.github.com>
  Date:   2017-03-03 (Fri, 03 Mar 2017)

  Changed paths:
    M index.bs

  Log Message:
  -----------
  Incorporate feedback from JeffH, part 3

Tag all instances of "client data", "authenticator data" and
"attestation data".