Unwanted conversion from string to integer in examples

[Mcourt]

Describe the bug
My examples are being converted to integers although they should be strings (ex: phone numbers).
This causes problem when validating my openapi file, as the parameter is set as "string" but has a number as example.

To Reproduce

1. Given this OpenAPI document

openapi: 3.0.0
info:
  title: My title
  version: 1.0.0
paths:
  /my/route:
    post:
      summary: My route
      requestBody:
        content:
          application/json:
            schema:
              type: object
              properties:
                phone:
                  type: string
                  example: "0612345678"
        required: true
      responses:
        '204':
          description: No Content
        '400':
          description: Bad Request
  

2. I execute the combine command
3. I get the following document (Notice the number example)

openapi: 3.0.0
info:
  title: My title
  version: 1.0.0
paths:
  /my/route:
    post:
      summary: My route
      requestBody:
        content:
          application/json:
            schema:
              type: object
              properties:
                phone:
                  type: string
                  example: 0612345678
        required: true
      responses:
        '204':
          description: No Content
        '400':
          description: Bad Request

Expected behavior
I expected my example to stay as a string.

[fabsrc]

This seems to be a bug in the js-yaml package.
See: nodeca/js-yaml#530

Tried it with your example:

node -e "console.log(require('js-yaml').safeDump({example: '0612345678'}))"
//  example: 0612345678

Using only digits below 8 (octal digits) seems to work fine:

node -e "console.log(require('js-yaml').safeDump({example: '0612345677'}))"
//  example: '0612345677'