Navigation bar is hidden after changeViewController

Hi guys,

I am using SlideMenuControllerSwift in my project. I have a problem with navigation bar. When I am going first time to 'MainViewController' is it working fine(navigation bar is visible), but when I choose from 'LeftMenu' same item 'MainViewController', navigation bar is hidden. What I am doing wrong? Thank you

AppDelegate

```
let storyboard = UIStoryboard(name: "Main", bundle: nil)

let mainViewController = storyboard.instantiateViewController(withIdentifier: "MainViewController") as! MainViewController
let leftViewController = storyboard.instantiateViewController(withIdentifier: "LeftMenuViewController") as! LeftMenuViewController
let StartViewController = storyboard.instantiateViewController(withIdentifier: "StartViewController") as! StartViewController
let nvc: UINavigationController = UINavigationController(rootViewController: StartViewController)

UINavigationBar.appearance().tintColor = UIColor.white

leftViewController.mainViewController = mainViewController

let slideMenuController = ExSlideMenuController(mainViewController:nvc, leftMenuViewController: leftViewController)
slideMenuController.automaticallyAdjustsScrollViewInsets = true
slideMenuController.delegate = mainViewController
self.window?.backgroundColor = UIColor(hex: "1F2E43")
self.window?.rootViewController = slideMenuController
self.window?.makeKeyAndVisible()
```

MainViewController

```
class MainViewController: RootViewController, SlideMenuControllerDelegate {

override func viewDidLoad() {
super.viewDidLoad()

// Do any additional setup after loading the view.
}

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
super.viewWillTransition(to: size, with: coordinator)
}

override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
self.addLeftBarButtonWithImage(UIImage(named: "MenuIcon")!)
self.slideMenuController()?.removeLeftGestures()
self.slideMenuController()?.addLeftGestures()
}

@IBAction func startAction(_ sender: AnyObject) {
}

override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}

}
```