Potentially incorrect number in the Shapley values section

[joaopalmeiro]

Hi! 👋

While reading the section on Shapley values, it seems to me that there's a typo at the beginning of "Examples and interpretation". In the "The sum of the contributions yields the difference between actual and average prediction (0.51)." sentence, shouldn't 0.51 actually be -0.31 (or round(diff.prediction, 2) in the code)?

Please let me know if I'm right or wrong, and if a correction is needed, whether I can open a PR.

Thanks!