Update Podfile and Podspec

* Update Podfile and Podspec with OneSignalXCFramework 3.6.0
* OneSignalXCFramework 3.6.0 enables the use of setLanguage on iOS

Author: tanaynigam

example/ios/Podfile

@@ -32,7 +32,7 @@ target 'Runner' do
 end
 
 target 'OneSignalNotificationServiceExtension' do
-  pod 'OneSignalXCFramework', '3.5.3'
+  pod 'OneSignalXCFramework', '3.6.0'
 end
 
 post_install do |installer|

ios/onesignal_flutter.podspec

@@ -13,7 +13,7 @@ Pod::Spec.new do |s|
   s.source_files = 'Classes/**/*'
   s.public_header_files = 'Classes/**/*.h'
   s.dependency 'Flutter'
-  s.dependency 'OneSignalXCFramework', '3.5.3'
+  s.dependency 'OneSignalXCFramework', '3.6.0'
   s.ios.deployment_target = '9.0'
   s.static_framework = true
 end