Update snippet structure to new template

snippets/unique_elements.md

@@ -1,5 +1,7 @@
-### unique_elements
-
+---
+title: unique_elements
+tags: list
+---
 Returns the unique elements in a given list.
 
 The given `list` is first converted to a `set` using the `set()` function. By definition, a `set` cannot have duplicate elements. So, the duplicate elements are automatically removed. Before returning, we convert it back to a `list`