Allow jpg output format

[johnreaganmoore]

Not sure if this is correct, but I want to be able to grab an image from a video and I think I need to be able to put an image file extension.

[johnreaganmoore]

    "timeline": {
        "tracks": [
            {
                "clips": [
                    {
                        "asset": {
                            "type": "video",
                            "src": "https://shotstack-assets.s3-ap-southeast-2.amazonaws.com/footage/skateboarding.mp4",
                            "trim": 2
                        },
                        "start": 0,
                        "length": 1
                    }
                ]
            }
        ]
    },
    "output": {
        "format": "jpg",
        "resolution": "hd"
    }
}

Support sent me that as an example of grabbing a screenshot, but I am not able to use jpg as an output format in the ruby sdk.

[jeffski]

Thanks for the pull request. We will be releasing a big update in the next week or two with all image formats and support for a heap of new features. I can merge this for now though so you aren't blocked.

[jeffski]

Thanks again @johnreaganmoore. Changes are merged and the gem has been deployed to RubyGems: https://rubygems.org/gems/shotstack.