Snippet format update

To match the starter (for the migration)

snippets/reject.md

@@ -1,4 +1,7 @@
-### reject
+---
+title: reject
+tags: array,beginner
+---
 
 Takes a predicate and array, like `Array.prototype.filter()`, but only keeps `x` if `pred(x) === false`.
 
@@ -9,4 +12,4 @@ const reject = (pred, array) => array.filter((...args) => !pred(...args));
 ```js
 reject(x => x % 2 === 0, [1, 2, 3, 4, 5]); // [1, 3, 5]
 reject(word => word.length > 4, ['Apple', 'Pear', 'Kiwi', 'Banana']); // ['Pear', 'Kiwi']
-```
+```