cargo fmt rust code (#1131)

* cargo fmt code

* Add empty line to seperate unrelated comments

* Fix review

* Update bubble_sort.rs

* Update merge_sort.rs

---------

Co-authored-by: Yudong Jin <krahets@163.com>

codes/rust/chapter_heap/top_k.rs

@@ -36,4 +36,4 @@ fn main() {
     let res = top_k_heap(nums, k);
     println!("最大的 {} 个元素为", k);
     print_util::print_heap(res.into_iter().map(|item| item.0).collect());
-}
+}