Update games.ipynb

[dhlee-work]

there are some 'def name' mismatches betweeen games.ipynb and games.py
I modifed the games.ipynb function names along games.py

minimax_decision -> minmax_decision
Canvas_minimax -> Canvas_min_max
alphabeta_search -> alpha_beta_search
Canvas_alphabeta -> Canvas_alpha_beta
alphabeta_player -> alpha_beta_player

Also,
In notebook.py, there is a error line.
super.init(varname, width, height, cid) is not proper for python 3.*
super().init(varname, width, height, cid) is more accurate.

Thank you !