Added support for projectId for riddle builder.

[milkovsky]

Currently it is not possible to set the projectId using the SDK during Riddle creation.

From the documentation::

{
    "type": "Poll",
    "projectId": 123,
    "build": {
        "title": "Favorite color poll",
        "blocks": [{
            "title": "What's your favorite color?",
            "type": "SingleChoice",
            "items": [
                "green",
                "red"
            ]
        }],
        "result": {
            "title": "Thank you",
            "description": "Thanks for your vote."
        }
    }
}

[philipp-riddle]

Hi milkovsky!
Thanks for your pull request and sorry for the delay! You are totally right. I will merge and release a new version.

Cheers,
Philipp