title: CollectionViewFlowLayout Issue
body: <p>when I am adding UICollectionViewFlowLayout file with collection view. collectionViewCell height is not increasing according to the collection view. it takes spacing from the top and bottom:</p>
  
  <p><img src="https://i.stack.imgur.com/u2Z5e.png" alt="image path"></p>
  
  <pre><code>- (void)awakeFromNib
  {
      [super awakeFromNib];
      self.itemSize = CGSizeMake((self.collectionView.frame.size.width/2)+100,self.collectionView.frame.size.height );
  
      //self.minimumInteritemSpacing = 10.0;
      self.minimumLineSpacing = 10.0;
      self.scrollDirection = UICollectionViewScrollDirectionHorizontal;
      self.sectionInset = UIEdgeInsetsMake(0, 30.0, 0, 30.0);
  }
  
  - (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity {
  
      NSInteger itemsCount = [self.collectionView.dataSource collectionView:self.collectionView numberOfItemsInSection:0];
  
      // Imitating paging behaviour
      //  previous offset and scroll direction
      if ((self.previousOffset &gt; self.collectionView.contentOffset.x) &amp;&amp; (velocity.x &lt; 0.0f)) {
          self.currentPage = MAX(self.currentPage - 1, 0);
  
      } else if ((self.previousOffset &lt; self.collectionView.contentOffset.x) &amp;&amp; (velocity.x &gt; 0.0f)) {
          self.currentPage = MIN(self.currentPage + 1, itemsCount - 1);
      }
  
      // Update offset by using item size + spacing
      CGFloat updatedOffset = (self.itemSize.width + 5) * self.currentPage;
      self.previousOffset = updatedOffset;
  
      return CGPointMake(updatedOffset, proposedContentOffset.y);
  }
  </code></pre>
  
  <p>i have created sub class of UICollectionViewLayout.</p>