Group up sameSite switch statement

[nikas-belogolov]

if (opt.sameSite) {
    var sameSite = typeof opt.sameSite === 'string'
      ? opt.sameSite.toLowerCase() : opt.sameSite;

    switch (sameSite) {
      case true:
      case 'strict':
        str += '; SameSite=Strict';
        break;
      case 'lax':
        str += '; SameSite=Lax';
        break;
      case 'none':
        str += '; SameSite=None';
        break;
      default:
        throw new TypeError('option sameSite is invalid');
    }
  }

[dougwilson]

We are slowly moving to StandardJS format which does not allow case fall through.