[webauthn] new commits pushed by emlun

The following commits were just pushed by emlun to https://github.com/w3c/webauthn:

* "with string-valued keys" => "whose keys are strings"

This helps avoid confusion by reading "string-valued keys" as "keys
mapped to values of string type".
  by Emil Lundberg
https://github.com/w3c/webauthn/commit/2c97d4cf8f7a7f59472d9e76570f8608941f14b0