[w3c/webauthn] ea30a3: Fix plural

  Branch: refs/heads/issue-644
  Home:   https://github.com/w3c/webauthn
  Commit: ea30a3319ac43765d8eef605fc49cbe66568f165
      https://github.com/w3c/webauthn/commit/ea30a3319ac43765d8eef605fc49cbe66568f165
  Author: Emil Lundberg <emil@yubico.com>
  Date:   2017-11-15 (Wed, 15 Nov 2017)

  Changed paths:
    M index.bs

  Log Message:
  -----------
  Fix plural