Snippet format update

To match the starter (for the migration)

snippets/averageBy.md

@@ -1,4 +1,7 @@
-### averageBy
+---
+title: averageBy
+tags: math,array,function,intermediate
+---
 
 Returns the average of an array, after mapping each element to a value using the provided function.
 
@@ -13,4 +16,4 @@ const averageBy = (arr, fn) =>
 ```js
 averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n); // 5
 averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 5
-```
+```