Minor bug due to a typo

[antonyomusabini]

Hi, Thanks for this great repo.

There is a minor bug due to a typo error in data.py file.

Line 37 should be: if downgrade in _downgrades_a and scale != 4: instead of if downgrade in _downgrades_b and scale != 4:

Best.

[krasserm]

if downgrade in _downgrades_b and scale != 4 seems to be correct. Why do you think it should be if downgrade in _downgrades_a and scale != 4.