Custom library doesn't load dependencies

The dependencies are not correct. You have to split name and owner like so:

    "dependencies": [
        {
            "name": "FastLED",
            "owner": "fastled",
            "version": "^3.3.0"
        },
        {
            "name": "ArduinoJson",
            "owner": "bblanchon",
            "version": "^6.18.0"
        }
    ]