updating DIRECTORY.md

Author: github-actions

DIRECTORY.md

@@ -167,6 +167,7 @@
       * [Test Doubly Linked List](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/linked_lists/doubly_linked_list/test_doubly_linked_list.py)
     * Singly Linked List
       * [Node](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/linked_lists/singly_linked_list/node.py)
+      * [Test Singly Linked Delete](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/linked_lists/singly_linked_list/test_singly_linked_delete.py)
       * [Test Singly Linked List](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/linked_lists/singly_linked_list/test_singly_linked_list.py)
       * [Test Singly Linked List Pairwise Swap](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/linked_lists/singly_linked_list/test_singly_linked_list_pairwise_swap.py)
       * [Test Singly Linked List Rotate](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/linked_lists/singly_linked_list/test_singly_linked_list_rotate.py)