title: Masonry: topLayoutGuide/bottomLayoutGuide cause crash in iOS9
body: <p>Masonry: topLayoutGuide/bottomLayoutGuide cause crash in iOS9</p>
  
  <p>Code in demo:  </p>
  
  <pre><code>[topView makeConstraints:^(MASConstraintMaker *make) {
      UIView *topLayoutGuide = (id)self.topLayoutGuide;
  
      // topLayoutGuide cause exception
      make.top.equalTo(topLayoutGuide.mas_bottom);
  
      make.left.equalTo(self.view);
      make.right.equalTo(self.view);
      make.height.equalTo(@40);
  }];
  </code></pre>