Fix issue trekhleb#132 - Wrong Red-Black Tree pictures in README.

Author: trekhleb

src/data-structures/tree/red-black-tree/README.md

@@ -74,15 +74,15 @@ unlike ordinary binary search trees.
 
 #### Left Right Case (See g, p and x)
 
-![Red Black Tree Balancing](https://www.geeksforgeeks.org/wp-content/uploads/redBlackCase3d.png)
+![Red Black Tree Balancing](https://www.geeksforgeeks.org/wp-content/uploads/redBlackCase3b.png)
 
 #### Right Right Case (See g, p and x)
 
 ![Red Black Tree Balancing](https://www.geeksforgeeks.org/wp-content/uploads/redBlackCase3c.png)
 
 #### Right Left Case (See g, p and x)
 
-![Red Black Tree Balancing](https://www.geeksforgeeks.org/wp-content/uploads/redBlackCase3c.png)
+![Red Black Tree Balancing](https://www.geeksforgeeks.org/wp-content/uploads/redBlackCase3d.png)
 
 ## References