Fix for invalid selector on iOS11 (#331)

Author: Valeour

ios/RNCPushNotificationIOS.m

@@ -258,7 +258,7 @@ - (void)handleRemoteNotificationRegistrationError:(NSNotification *)notification
   return RCTSettingsDictForUNNotificationSettings(settings.alertSetting == UNNotificationSettingEnabled,
                                                   settings.badgeSetting == UNNotificationSettingEnabled,
                                                   settings.soundSetting == UNNotificationSettingEnabled,
-                                                  settings.criticalAlertSetting == UNNotificationSettingEnabled,
+                                                  @available(iOS 12, *) && settings.criticalAlertSetting == UNNotificationSettingEnabled,
                                                   settings.lockScreenSetting == UNNotificationSettingEnabled,
                                                   settings.notificationCenterSetting == UNNotificationSettingEnabled,
                                                   settings.authorizationStatus);