fixed PSTCollectionViewCell backgroundView resizing
fixed PSTCollectionViewCell backgroundView resizing

jianwoo/PSTCollectionView,steipete/PSTCollectionView,Kevin775263419/PSTCollectionView,Amnysia/PSTCollectionView,niuxinghua/PSTCollectionView,StephaneDelcroix/PSTCollectionView,StephaneDelcroix/PSTCollectionView,godLoveLucifer/PSTCollectionView,thevuuranusls/PSTCollectionView,CorzFree/PSTCollectionView,Anish-kumar-dev/PSTCollectionView,ba01ei/PSTImprovedCollectionView,zjh171/PSTCollectionView,zace-yuan/PSTCollectionView