add rotate_RL() and rotate_RR() methods to AVL tree
add rotate_RL() and rotate_RR() methods to AVL tree

soliury/data-structure-with-js,LukeLin/data-structure-with-js,LukeLin/js-stl,sabrinaluo/data-structure-with-js,LukeLin/js-stl,LukeLin/data-structure-with-js