Add final newline back in iter/test.rs

Author: seanchen1991

src/iter/test.rs

@@ -2104,4 +2104,4 @@ fn check_update() {
     v.par_iter_mut().update(|v| v.push(0)).for_each(|_| ());
 
     assert_eq!(v, vec![vec![1, 0], vec![3, 2, 1, 0]]);
-}
+}