Snippet format update

To match the starter (for the migration)

snippets/differenceBy.md

@@ -1,4 +1,7 @@
-### differenceBy
+---
+title: differenceBy
+tags: array,function,intermediate
+---
 
 Returns the difference between two arrays, after applying the provided function to each array element of both.
 
@@ -14,4 +17,4 @@ const differenceBy = (a, b, fn) => {
 ```js
 differenceBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [1]
 differenceBy([{ x: 2 }, { x: 1 }], [{ x: 1 }], v => v.x); // [2]
-```
+```