ButtonBarView: Use defined identifier

Sources/ButtonBarView.swift

@@ -37,7 +37,7 @@ class ButtonBarView: UICollectionView {
     func setup() {
         scrollsToTop = false
         showsHorizontalScrollIndicator = false
-        register(UINib(nibName: "VLCLabelCell", bundle: .main), forCellWithReuseIdentifier:VLCLabelCell.cellIdentifier)
+        register(UINib(nibName: VLCLabelCell.cellIdentifier, bundle: .main), forCellWithReuseIdentifier:VLCLabelCell.cellIdentifier)
 
         separatorView = UIView(frame: CGRect(x: 0, y: self.frame.size.height - separatorHeight, width: self.frame.size.width, height: separatorHeight))
         addSubview(separatorView)