widdershins not resolving external $ref schema

widdershinsExample.yaml

swagger: '2.0'
info:
  title: Widdershins example
  description: Demonstrate $ref for external schema
  version: 0.1.0

schemes:
  - http

basePath: /widdershinsRefExample

paths:
  /example:
    get:
      summary: Return something
      description: Return something
      operationId: getExample
      responses:
        '200':
          description: OK
          schema:
            $ref: '#/definitions/response'

definitions:
  response:
    title: Response with external schema
    description: Response with external schema
    type: object
    properties:
      amount:
        description: A monetary amount.
        type: object
        allOf:
          - $ref: 'https://gist.githubusercontent.com/DavidBiesack/0753c16156df8d426256d85cb36c5585/raw/5a58be09cb0b83a5e7ad0fef92162a738a0a32ce/money.json'
      memo:
        description: An optional user-assigned memo.
        type: string