Snippet format update

To match the starter (for the migration)

snippets/URLJoin.md

@@ -1,4 +1,7 @@
-### URLJoin
+---
+title: URLJoin
+tags: string,utility,regexp,advanced
+---
 
 Joins all given URL segments together, then normalizes the resulting URL.
 
@@ -18,4 +21,4 @@ const URLJoin = (...args) =>
 
 ```js
 URLJoin('http://www.google.com', 'a', '/b/cd', '?foo=123', '?bar=foo'); // 'http://www.google.com/a/b/cd?foo=123&bar=foo'
-```
+```