composer.json

    "repositories": [
        {
            "type": "vcs",
            "url": "https://github.com/axe312ger/block_attributes"
        },
        {
            "type": "composer",
            "url": "https://packagist.drupal-composer.org"
        },
        {
            "type": "package",
            "package": {
                "name": "jackmoore/colorbox",
                "version": "1.6.3",
                "type": "drupal-library",
                "dist": {
                    "url": "https://github.com/jackmoore/colorbox/archive/1.6.3.zip",
                    "type": "zip"
                },
                "source": {
                    "url": "https://github.com/jackmoore/colorbox",
                    "type": "git",
                    "reference": "1.6.3"
                }
            }
        }
    ],