[VideoSubscriberAccount] Update bindings to Xcode 9.3 Beta 1 (#3348)

src/videosubscriberaccount.cs

@@ -259,6 +259,10 @@ namespace XamCore.VideoSubscriberAccount {
 
 		[Export ("tierIdentifiers", ArgumentSemantic.Copy)]
 		string[] TierIdentifiers { get; set; }
+
+		[TV (11,3), iOS (11,3)]
+		[NullAllowed, Export ("billingIdentifier")]
+		string BillingIdentifier { get; set; }
 	}
 
 	[TV (11,0)][iOS (11,0)]

tests/xtro-sharpie/iOS-VideoSubscriberAccount.todo

@@ -1,2 +0,0 @@
-!missing-selector! VSSubscription::billingIdentifier not bound
-!missing-selector! VSSubscription::setBillingIdentifier: not bound

tests/xtro-sharpie/tvOS-VideoSubscriberAccount.todo

@@ -1,2 +0,0 @@
-!missing-selector! VSSubscription::billingIdentifier not bound
-!missing-selector! VSSubscription::setBillingIdentifier: not bound