Fix rust compile warning and an obvious print error in array.rs (#1144)

* Fix rust compile warning and an obvious print error in array.rs

* Update LinkedList

1. drop unnessaray mut borrow
2. fmt code and make variable more readable

* follow convention of this repo

* Update list_node.rs

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

codes/rust/chapter_array_and_linkedlist/array.rs

@@ -90,7 +90,7 @@ fn main() {
     // 长度扩展
     let mut nums = extend(nums, 3);
     print!("将数组长度扩展至 8 ，得到 nums = ");
-    print_util::print_array(&arr);
+    print_util::print_array(&nums);
 
     // 插入元素
     insert(&mut nums, 6, 3);