Swagger ignores vendorextention for $ref type properties

Hi @wing328 ,

Swagger ignores vendorextention for $ref type properties. For e.g. If there is a property as follows in yaml

  myObject:
       properties:
               myid:
                  type: int
                  x-app-extensions: {"aaid" : "bb", "ccid" : "dd"}
errors:
                   x-app-extensions: {"aaerr" : "bb", "ccerr" : "dd"}
    $ref: "#/definitions/errorModel"

Then, swagger model ignores vendorextensions for errors, and only has only $ref property in the parsed json node, and same in reflected in created java model. But, vendorextenion is correctly picked up for myid. The ignorance of vendor extension is due to an issue in following snippet of the code of io.swagger.util.PropertyDeserializer.propertyFromNode(JsonNode) method.

   JsonNode detailNode = node.get("$ref");
  if (detailNode != null) {
      return new RefProperty(detailNode.asText()).description(description);
  }

Is it expected that, $ref type nodes are not supposed to have any other properties?