Snippet format update

To match the starter (for the migration)

snippets/isNil.md

@@ -1,4 +1,7 @@
-### isNil
+---
+title: isNil
+tags: type,beginner
+---
 
 Returns `true` if the specified value is `null` or `undefined`, `false` otherwise.
 
@@ -11,4 +14,4 @@ const isNil = val => val === undefined || val === null;
 ```js
 isNil(null); // true
 isNil(undefined); // true
-```
+```