Updating training notebooks - peak_local_max function kwarg deprecated

[GenevieveBuckley]

Cell 20 in lesson notebook 02_interactive_analysis.ipynb needs updating to be compatible with the latest versions of scikit-image and numpy. I know this notebook was written several years ago, but it's a great example and I'd like to keep it useable for everyone.

It needs to be:

Now we can try and identify the centers of each of the nuclei by finding peaks of the distance transform

peaks = feature.peak_local_max(
    smoothed_distance,
    footprint=np.ones((7, 7), dtype=bool),
    labels=measure.label(foreground_processed)
)

There are two changes here:

1. The indices keyword argument for peak_local_max has been deprecated. I have removed it. This also means the returned result is the peaks variable, not peaks_local_max as before.
2. Dtypes of np.bool are deprecated, and it's advised to replace with bool instead. I've done that here.