small change to support higher numpy versions

[kilojoules]

No description provided.

[kilojoules]

AttributeError: module 'numpy' has no attribute 'int'.
`np.int` was a deprecated alias for the builtin `int`. To avoid this error in existing code, 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.
The aliases was originally deprecated in NumPy 1.20; for more details and guidance see the original release note at:
    https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations

[kilojoules]

This is very similar to #15. I have made my own fork that I am planning to maintain https://github.com/kilojoules/sliced/ but I am open to discussing with the community where the new code base should live