invalidate(callback) {
		if (callback) {
			asyncLib.each(
				this.watchings,
				(watching, callback) => watching.invalidate(callback),
				callback
			);
		} else {
			for (const watching of this.watchings) {
				watching.invalidate();
			}
		}
	}
@param {Callback<void>=} callback signals when the build has completed again
@returns {void}