readOnly attribute not rendered as property metadata

Q	A
Bug or feature request?	Bug
Which Swagger/OpenAPI version?	3.0.0
Which Swagger-UI version?	3.9.2
How did you install Swagger-UI?	NPM
Which browser & version?	Google Chrome, 63.0.3239.132 (Official Build) (64-bit)
Which operating system?	MacOS X 10.13.2

Demonstration API definition

openapi: 3.0.0
info:
  version: 1.0.0
  title: Test
paths:
  /plan:
    post:
      summary: Creates a Test
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/Test'
      responses:
        '201':
          description: Created
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Test'
components:
  schemas:
    SomeSchema:
      required:
        - hello
      properties:
        hello:
          type: string
    Test:
      required:
        - field1
        - field2
      properties:
        field1:
          type: string
        field2:
          allOf:
            - $ref: '#/components/schemas/SomeSchema'
          readOnly: true

Configuration (browser query string, constructor, config.yaml)

n.a.

Expected Behavior

Request Body Model should match Example value:

{
  "field1": "string"
}

Current Behavior

Request Body Model shows field2 as well:

It is not visible that this field is readOnly.

Possible Solution

Context

Reproduce the supplied OpenAPI 3 YAML in Swagger UI and inspect how the request-body model handles the nested readOnly property. Compare the rendered request example with the expected behavior, then verify that the readOnly field is excluded from the request model and its metadata is visible.