updating DIRECTORY.md

Author: cclauss

DIRECTORY.md

@@ -481,6 +481,7 @@
   * [Longest Increasing Subsequence Iterative](dynamic_programming/longest_increasing_subsequence_iterative.py)
   * [Longest Increasing Subsequence O Nlogn](dynamic_programming/longest_increasing_subsequence_o_nlogn.py)
   * [Longest Palindromic Subsequence](dynamic_programming/longest_palindromic_subsequence.py)
+  * [Longest Repeating Subsequence](dynamic_programming/longest_repeating_subsequence.py)
   * [Matrix Chain Multiplication](dynamic_programming/matrix_chain_multiplication.py)
   * [Matrix Chain Order](dynamic_programming/matrix_chain_order.py)
   * [Max Non Adjacent Sum](dynamic_programming/max_non_adjacent_sum.py)