code: function(expMonth, expYear, success, error) {
      success = success || noop;
      error = error || noop;
      exec(success, error, "CordovaStripe", "validateExpiryDate", [expMonth, expYear]);
    }
docs: Validates the expiry date of a card
  @param {number} expMonth Expiry month
  @param {number} expYear Expiry year
  @param {Function} success
  @param {Function} error