Add rpb2 vocabulary to labels.json.
Add rpb2 vocabulary to labels.json.

See https://github.com/hbz/lobid-rdf-to-json/issues/30#issuecomment-256364245

jschnasse/regal-api,edoweb/regal-api,hbz/lobid-rdf-to-json,edoweb/regal-api,jschnasse/regal-api,edoweb/regal-api,jschnasse/regal-api,edoweb/regal-api,jschnasse/regal-api