[iOS] update requestPermission

example/ios/Runner/Runner.entitlements

+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>com.apple.security.application-groups</key>
+	<array/>
+</dict>
+</plist>

ios/Classes/strategies/NotificationPermissionStrategy.m

@@ -23,10 +23,9 @@
     completionHandler(status);
     return;
   }
-  
+  dispatch_async(dispatch_get_main_queue(), ^{
     if(@available(iOS 10.0, *)) {
       UNUserNotificationCenter *center = [UNUserNotificationCenter currentNotificationCenter];
-    
       UNAuthorizationOptions authorizationOptions = 0;
       authorizationOptions += UNAuthorizationOptionSound;
       authorizationOptions += UNAuthorizationOptionAlert;
@@ -36,7 +35,6 @@
           completionHandler(PermissionStatusDenied);
           return;
         }
-      completionHandler(PermissionStatusGranted);
       }];
     } else {
       UIUserNotificationType notificationTypes = 0;
@@ -45,8 +43,10 @@
       notificationTypes |= UIUserNotificationTypeBadge;
       UIUserNotificationSettings *settings = [UIUserNotificationSettings settingsForTypes:notificationTypes categories:nil];
       [[UIApplication sharedApplication] registerUserNotificationSettings:settings];
-    completionHandler(PermissionStatusGranted);
     }
+    [[UIApplication sharedApplication] registerForRemoteNotifications];
+    completionHandler(PermissionStatusGranted);
+  });
 }
 
 + (PermissionStatus)permissionStatus {