chapter 3, xlsx example and in2csv

[kurokirasama]

The url https://www.nporadio2.nl/data/download/TOP-2000-2020.xlsx no longers works

And, in2csv --names gives this message:

/usr/lib/python3/dist-packages/openpyxl/compat/numbers.py:41: DeprecationWarning: `np.float` is a deprecated alias for the builtin `float`. To silence this warning, use `float` by itself. Doing this will not modify any behavior and is safe. If you specifically wanted the numpy scalar type, use `np.float64` here.
Deprecated in NumPy 1.20; for more details and guidance: https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations

I tried outside the docker image and in2csv works fine