public function getDrushMajorVersion() {
    $version_info = json_decode($this->executor->drush('version --format=json')->run()->getMessage(), TRUE);
    if (!empty($version_info['drush-version'])) {
      $version = $version_info['drush-version'];
    }
    else {
      $version = $version_info;
    }

    $major_version = substr($version, 0, 1);

    return (int) $major_version;
  }