[OpenAPI 3.1.0 support] JsonSchema type changes not handled.

[DrSatyr]

While migration to OpenAPI 3.1.0 all Schema objects becomes JsonSchema. 3.1.0 deserializes schema "type" to array field "types". At least this part of SchemaDiff works incorrectly: SchemaDiff.java#L349-L352. Most probably such changes will affect other parts of library.