Format snippets

snippets/flatten.md

@@ -12,7 +12,11 @@ Flattens an array up to the specified depth.
 
 ```js
 const flatten = (arr, depth = 1) =>
-  arr.reduce((a, v) => a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v), []);
+  arr.reduce(
+    (a, v) =>
+      a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v),
+    []
+  );
 ```
 
 ```js