[MC-57713] Double plant JSON is malformed

The .json file for double_plant is malformed. It is missing commas, and duplicates keys for the "variants" object.

Code below from latest snapshot:

{
    "__comment": "Fair warning, this format is highly likely to change even more in the future!",
    "variants": {
        "bottom": { "model": "double_sunflower_bottom" },
        "top":    { "model": "double_sunflower_top" }
        "bottom": { "model": "double_syringa_bottom" },
        "top":    { "model": "double_syringa_top" }
        "bottom": { "model": "double_grass_bottom" },
        "top":    { "model": "double_grass_top" }
        "bottom": { "model": "double_fern_bottom" },
        "top":    { "model": "double_fern_top" }
        "bottom": { "model": "double_rose_bottom" },
        "top":    { "model": "double_rose_top" }
        "bottom": { "model": "double_paeonia_bottom" },
        "top":    { "model": "double_paeonia_top" }
    }
}