Deprecation warning for np.int in _vertical_x()

[davidwagner]

Low-priority: make test shows the following deprecation warning:

tests/test_tables.py::test_hist_of_counts
  /home/daw/datascience/datascience/datascience/tables.py:5799: 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
    ticks = np.rint(ticks).astype(np.int)

It appears that np.int should be converted to int.