Update demo.py

fix error:
错误：Traceback (most recent call last):
File “C:\Users\mew\Desktop\libMA-master\demo.py”, line 226, in
main()
File “C:\Users\mew\Desktop\libMA-master\demo.py”, line 151, in main
atk=atk_dict[fairy_name]) or build_roundtable()
File “C:\Users\mew\Desktop\libMA-master\demo.py”, line 51, in build_roundtable
for i in range(rounds):
TypeError: range() integer end argument expected, got float.