Add findLastIndex, update findLast

snippets/findLast.md

@@ -5,7 +5,7 @@ Returns the last element for which the provided function returns a truthy value.
 Use `Array.filter()` to remove elements for which `fn` returns falsey values, `Array.slice(-1)` to get the last one.
 
 ```js
-const findLast = (arr, fn) => arr.filter(fn).slice(-1);
+const findLast = (arr, fn) => arr.filter(fn).slice(-1)[0];
 ```
 
 ```js