Shadow disappears before closing

Hi!
I've noticed that side shadow disappears before closing menu animation ends.
It happens on both sides.

I've fixed it with this implementation of `CloseMenu` in _Sidebar.cs_

```

public void CloseMenu(bool animate = true)
{
if (!IsOpen || Disabled)
return;
MenuViewController.View.EndEditing(true);

UIView.AnimateNotify(animate ? Sidebar.SlideSpeed : 0,
0,
UIViewAnimationOptions.CurveEaseInOut,
() =>
{
_sidebarContentArea.CloseAnimation();
_sidebarContentArea.AfterCloseAnimation(TapGesture);
IsOpen = false;
},
(finished) =>
{
if (finished)
HideShadow();
});
}
```

Basically same as original but used `AnimateNotify` wrapper to have completion handler