Snippet format update

To match the starter (for the migration)

snippets/isString.md

@@ -1,4 +1,7 @@
-### isString
+---
+title: isString
+tags: type,string,beginner
+---
 
 Checks if the given argument is a string. Only works for string primitives.
 
@@ -10,4 +13,4 @@ const isString = val => typeof val === 'string';
 
 ```js
 isString('10'); // true
-```
+```