Chapter 2: SettingWithCopyWarning

Thanks for the good book, currently I'm reading the second chapter and at some points my results are not the same as the notebook (pretty much all of the predictions). I think the reason could be cell 30:
```
for set_ in (strat_train_set, strat_test_set):
set_.drop("income_cat", axis=1, inplace=True)
```
which throws the warning in the title.