fix: right-left and left-right inversion for the English version of AVL Tree (#1448)

* Fix right-left and left-right inversion on AVL Binary Tree

* Update avl_tree.md

* Update avl_tree.md

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

en/docs/chapter_tree/avl_tree.md

@@ -289,17 +289,17 @@ It can be observed that **the right and left rotation operations are logically s
 [file]{avl_tree}-[class]{avl_tree}-[func]{left_rotate}
 ```
 
-### Right-left rotation
+### Left-right rotation
 
 For the unbalanced node 3 shown in the figure below, using either left or right rotation alone cannot restore balance to the subtree. In this case, a "left rotation" needs to be performed on `child` first, followed by a "right rotation" on `node`.
 
-![Right-left rotation](avl_tree.assets/avltree_left_right_rotate.png)
+![Left-right rotation](avl_tree.assets/avltree_left_right_rotate.png)
 
-### Left-right rotation
+### Right-left rotation
 
 As shown in the figure below, for the mirror case of the above unbalanced binary tree, a "right rotation" needs to be performed on `child` first, followed by a "left rotation" on `node`.
 
-![Left-right rotation](avl_tree.assets/avltree_right_left_rotate.png)
+![Right-left rotation](avl_tree.assets/avltree_right_left_rotate.png)
 
 ### Choice of rotation