kin-openapi external references bug

ext.json

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "definitions": {
        "a": {
            "type": "string"
        },
        "b": {
            "type": "object",
            "description": "I use a local reference.",
            "properties": {
                "name": {
                    "$ref": "#/definitions/a"
                }
            }
        }
    }
}

extref_test.go

package test

import (
	"testing"

	"github.com/getkin/kin-openapi/openapi3"
)

func TestExternalRef(t *testing.T) {
	loader := &openapi3.SwaggerLoader{
		IsExternalRefsAllowed: true,
	}
	_, err := loader.LoadSwaggerFromFile("spec.yaml")
	if err != nil {
		t.Error(err)
	}
}

spec.yaml

openapi: 3.0.1
components:
  schemas:
    Test:
      type: object
      properties:
        test:
          $ref: 'ext.json#/definitions/b'