Remove weak modifier (fixes issue #190) (#203)

Author: rostopira

Sources/ParseLiveQuery/Internal/ClientPrivate.swift

@@ -33,7 +33,7 @@ private func parseObject<T: PFObject>(_ objectDictionary: [String:AnyObject]) th
 
 extension Client {
     class SubscriptionRecord {
-        weak var subscriptionHandler: AnyObject?
+        var subscriptionHandler: AnyObject?
         // HandlerClosure captures the generic type info passed into the constructor of SubscriptionRecord,
         // and 'unwraps' it so that it can be used with just a 'PFObject' instance.
         // Technically, this should be a compiler no-op, as no witness tables should be used as 'PFObject' currently inherits from NSObject.