Update snippet structure to new template

snippets/palindrome.md

@@ -1,5 +1,7 @@
-### palindrome
-
+---
+title: palindrome
+tags: string
+---
 Returns `True` if the given string is a palindrome, `False` otherwise.
 
 Convert string `str.lower()` and use `re.sub` to remove non-alphanumeric characters from it. Then compare the new string to the reversed.