Valid datetimes are not accepted by JSON validator

When validating a field, the validate method of com.github.fge.jsonschema.main is called, passing a JsonNode that contains the date as its value. This method throws a JSON parsing exception for some date-times that are valid according to OpenAPI data types spec.

As described in RFC3339, both 1985-04-12T23:20:50.52Z and 1985-04-12T23:20:50.52+08:00 are valid datetime examples, the first is correctly parsed, the second no.