The default value of useNativeTypes has been changed to false

Even with useNativeTypes set to false, strings will not be typed with xsd:string.

For the moment, both produceGeneralizedRdf and produceGeneralizedRDF are accepted as flag names for the toRDF algorithm. See https://github.com/json-ld/json-ld.org/commit/d6460dcef6fa207302e5d3912a44fdffd603669f#commitcomment-4015838