title: Label not change in callback swift 3
body: <p>I want to change my label text after getting a response from the server but it doesn't change after getting a response from server!!</p>
  
  <p>here is my code :</p>
  
  <pre><code>func getOrderCost() {
  
      DispatchQueue.main.async {
  
          self.customView?.setOrderPriceEstimate(price: "۰")
          var price = 10
          if let p_code = self.customView?.getPromotionCode() {
  
              self.orderPriceObject.promotion_code = p_code
          }  
          self.registerOrderVM.getOrderPriceEstimation(orderInfo: self.orderPriceObject).asObservable().subscribe(onNext: { (response) in
  
              if let res = response as? [String: Int], let p = res["price_with_added_value"] {
  
                  self.customView?.setOrderPriceEstimate(price: "cost : \(p)")
              }
          }, onError: { (error) in
  
              self.view.showMessage(error.localizedDescription, type: .error, options: [.hideOnTap(true)])
          }).disposed(by: self.disposeBag)
      }
  }
  </code></pre>
  
  <p>and this is the <code>setOrderPriceEstimate</code> function in <code>customView</code> :</p>
  
  <pre><code>public func setOrderPriceEstimate(price: String) {
  
      self.orderCostLbl.text = price
  }
  </code></pre>