使用wkwebview时，push后，再pop返回，报错

Cannot form weak reference to instance (xxxx) of class xxxx. It is possible that this object was over-released, or is in the process of deallocation

原因是给webView.scrollView设置了代理：webView.scrollView.delegate = self ；

解决办法：

-(void)dealloc { webView.scrollView.delegate = nil; }

by：初光夫