title: Warning frame for "Navigation bar" will be different at run time appears in Xcode 8 Swift 3
body: <p>Before I've upgraded to <code>Xcode 8</code> I haven't seen this error in such case. I have different Navigation Controllers. For all of them I see an error <code>Frame for "Navigation bar" will be different at the run time. Navigation bar "Expected: width=384, Actual: width=375</code>. In reality these Navigation Controllers doesn't have <code>Navigation bar</code>. <code>Navigation bar</code> exists for subviews. Anyway I could solve it by tick and untick the checkbox <code>Shows navigation bar</code> in <code>Attributes inspector</code>. But unfortunately every time I reopen <code>Main.storyboard</code> this warning appears again. Also if I click on yellow triangle and then on update frames nothing happen.</p>
  
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