Snippet format update

To match the starter (for the migration)

snippets/similarity.md

@@ -1,4 +1,7 @@
-### similarity
+---
+title: similarity
+tags: array,math,beginner
+---
 
 Returns an array of elements that appear in both arrays.
 
@@ -10,4 +13,4 @@ const similarity = (arr, values) => arr.filter(v => values.includes(v));
 
 ```js
 similarity([1, 2, 3], [1, 2, 4]); // [1, 2]
-```
+```