composer.json

{
    "name": "fweber/bla",
    "authors": [
        {
            "name": "Florian Weber",
            "email": "[email protected]"
        }
    ],
    "extra": {
        "installer-types": ["library"],
        "installer-paths": {
            "your/custom/path/{$name}/": ["dawehner/lazysizes"],
            "libraries/{$name}/": ["ckeditor/ckeditor"]
        }
    },
    "require": {
        "oomphinc/composer-installers-extender": "^1.1",
        "ckeditor/ckeditor": "^4.5",
        "dawehner/lazysizes": "dev-master"
    }
}