Update fake petstore spec with more `example`

[wing328]

Description

Add example to fake petstore to cover more edge cases.

Ref: https://gist.github.com/spr3nk3ls/f165f0f19656a9e1ef8bf0f900f5067a

Swagger-codegen version

Latest master

Related issues

#5247

Suggest a Fix

Add the example in https://gist.github.com/spr3nk3ls/f165f0f19656a9e1ef8bf0f900f5067a#file-swagger_example-json-L64 to fake petstore spec.