[webauthn] choose consistent section id prefix

equalsJeffH has just created a new issue for https://github.com/w3c/webauthn:

== choose consistent section id prefix ==
we are presently using at least two section id prefixes:
`#sec-`
`#sctn-`
..and there's many section ids with no discernable prefix (which invites collisions).

I prefer `#sctn-` because it is not a abbreviation of "security", which is what I think when I see `#sec-`.

Anyway, WDYT?


Please view or discuss this issue at https://github.com/w3c/webauthn/issues/704 using your GitHub account