`3_keras_basic_feat_eng.ipynb`, `get_scal` does nothing

Wrong indentation on last line of `get_scal` definition means that function returns `None` instead of
returning the `minmax` closure.

Correct code would be:

```
def get_scal(feature):
def minmax(x):
mini = train[feature].min()
maxi = train[feature].max()
return (x - mini)/(maxi-mini)
return(minmax)
```

https://github.com/GoogleCloudPlatform/training-data-analyst/blob/ec4838a9f532185dcf98a82530b443252d8ae830/courses/machine_learning/deepdive2/feature_engineering/solutions/3_keras_basic_feat_eng.ipynb?short_path=7965270#L883

And

https://github.com/GoogleCloudPlatform/training-data-analyst/blob/ec4838a9f532185dcf98a82530b443252d8ae830/courses/machine_learning/deepdive2/feature_engineering/solutions/3_keras_basic_feat_eng.ipynb?short_path=7965270#L1629