Update CSStickyHeaderFlowLayout.m
Update CSStickyHeaderFlowLayout.m

Fixing warning: subclass is modifying attributes returned by UICollectionViewFlowLayout without copying them
CSStickyHeaderFlowLayout/CSStickyHeaderFlowLayout,jamztang/CSStickyHeaderFlowLayout,iException/CSStickyHeaderFlowLayout,CSStickyHeaderFlowLayout/CSStickyHeaderFlowLayout,jamztang/CSStickyHeaderFlowLayout,iException/CSStickyHeaderFlowLayout,jamztang/CSStickyHeaderFlowLayout,iException/CSStickyHeaderFlowLayout,CSStickyHeaderFlowLayout/CSStickyHeaderFlowLayout