code: function is(store, uri, type) {
    var ret = false
  
    var types = store.findTypeURIs($rdf.sym(uri))
  
    if (types && types[type]) {
      ret = true
    }
  
    return ret
  }
docs: See if a URI is a certain type
  @param  {object}  store the rdflib store
  @param  {string}  uri   the uri to check
  @param  {string}  type  the type to test
  @return {Boolean}       true if uri is that type