Respect allOf when generating mocked responses.

[sammarks]

In my usage of this library, I'll run into something similar to the following schema:

{
    "type": "object",
    "required": ["name", "photoUrls"],
    "allOf": [
        {
            "type": "object",
            "properties": {
                "test-one": {
                    "type": "integer",
                    "format": "int64"
                }
            }
        },
        {
            "type": "object",
            "properties": {
                "test-two": {
                    "type": "integer",
                    "format": "int64",
                    "example": 20
                }
            }
        }
    ],
    "properties": {
        "id": {
            "type": "integer",
            "format": "int64"
        },
        "category": {
            "$ref": "#/definitions/Category"
        },
        "name": {
            "type": "string",
            "example": "doggie"
        },
        "photoUrls": {
            "type": "array",
            "xml": {
                "name": "photoUrl",
                "wrapped": true
            },
            "items": {
                "type": "string"
            }
        },
        "tags": {
            "type": "array",
            "minItems": 2,
            "maxItems": 5,
            "xml": {
                "name": "tag",
                "wrapped": true
            },
            "items": {
                "$ref": "#/definitions/Tag"
            }
        },
        "status": {
            "type": "string",
            "description": "pet status in the store",
            "enum": ["available", "pending", "sold"]
        }
    },
    "xml": {
        "name": "Pet"
    }
}

Currently, the library doesn't generate values for test-one or test-two since they're hidden inside the allOf clause of the schema. This PR updates the response mocker to respect the allOf clause and generate values for it as well.

[enmand]

Any change on getting this merged in, and a new NPM release up? 🙏