updating DIRECTORY.md

Author: github-actions

DIRECTORY.md

@@ -291,10 +291,13 @@
   * [AlternativeStringArrange](https://github.com/TheAlgorithms/Javascript/blob/master/String/AlternativeStringArrange.js)
   * [CheckAnagram](https://github.com/TheAlgorithms/Javascript/blob/master/String/CheckAnagram.js)
   * [CheckCamelCase](https://github.com/TheAlgorithms/Javascript/blob/master/String/CheckCamelCase.js)
+  * [CheckFlatCase](https://github.com/TheAlgorithms/Javascript/blob/master/String/CheckFlatCase.js)
+  * [CheckKebabCase](https://github.com/TheAlgorithms/Javascript/blob/master/String/CheckKebabCase.js)
   * [CheckPalindrome](https://github.com/TheAlgorithms/Javascript/blob/master/String/CheckPalindrome.js)
   * [CheckPangram](https://github.com/TheAlgorithms/Javascript/blob/master/String/CheckPangram.js)
   * [CheckPascalCase](https://github.com/TheAlgorithms/Javascript/blob/master/String/CheckPascalCase.js)
   * [CheckRearrangePalindrome](https://github.com/TheAlgorithms/Javascript/blob/master/String/CheckRearrangePalindrome.js)
+  * [CheckSnakeCase](https://github.com/TheAlgorithms/Javascript/blob/master/String/CheckSnakeCase.js)
   * [CheckVowels](https://github.com/TheAlgorithms/Javascript/blob/master/String/CheckVowels.js)
   * [CheckVowels](https://github.com/TheAlgorithms/Javascript/blob/master/String/CheckVowels.test.js)
   * [CheckWordOccurrence](https://github.com/TheAlgorithms/Javascript/blob/master/String/CheckWordOccurrence.js)