UNTP ontology: error confusion between IRI and string

See this line https://opensource.unicc.org/un/unece/uncefact/spec-untp/-/blob/aa7548da70f74d24a21e908806c926b6a55a3c57/artefacts/vocabularies/untp-core/untp-ontology.jsonld#L71

"rdfs:subClassOf": "untp:VerifiableCredential",

The object of the statement is here a string (NOK). It should be an IRI.

We should have this instead:

"rdfs:subClassOf": { @id: "untp:VerifiableCredential" },

Same error occurs a number of times in the ontology.