updating DIRECTORY.md

Author: Ramy-Badr-Ahmed

DIRECTORY.md

@@ -21,11 +21,11 @@
     * [Avltree](./DataStructures/AVLTree/AVLTree.php)
     * [Avltreenode](./DataStructures/AVLTree/AVLTreeNode.php)
     * [Treetraversal](./DataStructures/AVLTree/TreeTraversal.php)
-* Binarysearchtree
+  * Binarysearchtree
     * [Binarytreetraversal](./DataStructures/BinarySearchTree/BinaryTreeTraversal.php)
     * [Bstnode](./DataStructures/BinarySearchTree/BSTNode.php)
     * [Bstree](./DataStructures/BinarySearchTree/BSTree.php)
-    * [Duplicatekeyexception](./DataStructures/BinarySearchTree/DuplicateKeyException.php)    
+    * [Duplicatekeyexception](./DataStructures/BinarySearchTree/DuplicateKeyException.php)
   * Disjointsets
     * [Disjointset](./DataStructures/DisjointSets/DisjointSet.php)
     * [Disjointsetnode](./DataStructures/DisjointSets/DisjointSetNode.php)