title: CloudKit. Token change block of CKFetchRecordZoneChangesOperation not called
body: <p>I am trying to implement syncing with CloudKit. 
  To fetch changes from the server i am using CKFetchRecordZoneChangesOperation. 
  However recordZoneChangeTokensUpdatedBlock not called at all. 
  Here is the code: </p>
  
  <pre><code>let options = CKFetchRecordZoneChangesOptions()
  options.previousServerChangeToken = changesToken
  
  let operation = CKFetchRecordZoneChangesOperation(recordZoneIDs: [paletteZoneId], optionsByRecordZoneID: [paletteZoneId:options])
  operation.fetchAllChanges = true
  
  operation.recordChangedBlock = {(record) in
     ...
  }
  
  operation.recordWithIDWasDeletedBlock = { (recordId,str) in
      ...
  }
  
  operation.recordZoneChangeTokensUpdatedBlock = { recordZoneId, token, data in
      print("new token")
      self.changesToken = token
  }
  
  
  operation.fetchRecordZoneChangesCompletionBlock = { error in
      ...
  }
  
  privateDB.add(operation)
  </code></pre>
  
  <p>So as the result operation is not working properly. Other blocks are called as expected.</p>
  
  <p>Documentation says that token block should be called per zone, but it is not called at all. </p>
  
  <p>I would really appreciate any help.</p>
  
  <p>Many thanks.</p>