Allow Symbol keyed Hash in LinkedDataSignature (#4715)
Allow Symbol keyed Hash in LinkedDataSignature (#4715)

SerializarbleResource#as_json serializes to Symbol keyed Hash, but current
implementation of LinkedDataSignature expects String keyed Hash.

So it generates broken payload.
Arukas/mastodon,Arukas/mastodon,Arukas/mastodon,Arukas/mastodon