Bug : mock mode return string not compliant ( missing " " )

[LasneF]

given this spec

openapi: 3.0.0
info:
  title: Sample API
  description: Optional multiline or single-line description in [CommonMark](http://commonmark.org/help/) or HTML.
  version: 0.1.9



paths:
  /toto:
    get:
      responses:
        "200": # status code
          description: A JSON array of user names
          content:
            application/json:
              schema:
                  type: string

GET /toto

return bob , should return "bob" it misses the " so it is not valid json

notice that when changing the schema to

type : object
properties :
"jo" :
type : string

it returns correctly { "jo" : "bob" }