重写UICollectionViewFlowLayout报cache mismatched frame警告
在重写UICollectionViewFlowLayout的时候会有很多坑，比如：
Logging only once for UICollectionViewFlowLayout cache mismatched frame
UICollectionViewFlowLayout has cached frame mismatch for index path <NSIndexPath: 0xc000000000200016> {length = 2, path = 0 - 1} - cached value: {{85, 40}, {55, 30}}; expected value: {{89, 40}, {55, 30}}
This is likely occurring because the flow layout subclass RHCollectionViewFlowLayout is modifying attributes returned by UICollectionViewFlowLayout without copying them
这个警告的大致原因是：返回的数组时，没有使用该数组的拷贝对象，而是直接使用了该数组。找了一圈资料，大部分是说需要进行深拷贝。
emmm...该方案是可行的，只是大部分找错了地方。
stackoverflow解决方案中找到了匹配的解决方法：
在- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath方法中
将：UICollectionViewLayoutAttributes * currentItemAttributes = [super layoutAttributesForItemAtIndexPath:indexPath];
改成：UICollectionViewLayoutAttributes * currentItemAttributes = [[super layoutAttributesForItemAtIndexPath:indexPath] copy];
