public function defaultOptions(Command $command) {
    $command->addOption('config', 'c', InputOption::VALUE_REQUIRED, 'Configuration file to be used instead of default `robo.yml.dist`.', 'robo.yml');
    $command->addOption('override', 'o', InputOption::VALUE_REQUIRED | InputOption::VALUE_IS_ARRAY, 'Configuration value(s) to be overridden. Format: "path.to.key:value"', []);
  }