[short_path] Fix DeprecationWarning

[kuramogura]

Fix the following warning.

DeprecationWarning: `np.int` is a deprecated alias for the builtin `int`. To silence this warning, use `int` by itself. Doing this will not modify any behavior and is safe. When replacing `np.int`, you may wish to use e.g. `np.int64` or `np.int32` to specify the precision. If you wish to review your current use, check the release note link for additional information.
Deprecated in NumPy 1.20; for more details and guidance: https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations
  J = np.zeros_like(nodes, dtype=np.int)

[mmcky]

thanks @kuramogura

[jstac]

Thanks @kuramogura , looks good to me.

If you have time, similar PRs for the Python lectures on quantecon.org would be greatly appreciated ;-)