updating DIRECTORY.md

Author: github-actions

DIRECTORY.md

@@ -13,6 +13,7 @@
 ## Ciphers
  * [CaesarsCipher](https://github.com/TheAlgorithms/Javascript/blob/master/Ciphers/CaesarsCipher.js)
  * [KeyFinder](https://github.com/TheAlgorithms/Javascript/blob/master/Ciphers/KeyFinder.js)
+ * [ROT13](https://github.com/TheAlgorithms/Javascript/blob/master/Ciphers/ROT13.js)
  * [VigenereCipher](https://github.com/TheAlgorithms/Javascript/blob/master/Ciphers/VigenereCipher.js)
  * [XORCipher](https://github.com/TheAlgorithms/Javascript/blob/master/Ciphers/XORCipher.js)