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

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

codes/rust/chapter_tree/array_binary_tree.rs

@@ -196,4 +196,4 @@ fn main() {
     println!("中序遍历为：{:?}", res);
     res = abt.post_order();
     println!("后序遍历为：{:?}", res);
-}
+}