Fix np.bool NumPy 1.20 deprecation error.

[kikefdezl]

In utils.py, line 54, we reference np.bool, which causes this error:

AttributeError: module 'numpy' has no attribute 'bool'.
`np.bool` was a deprecated alias for the builtin `bool`. To avoid this error in existing code, use `bool` by itself. Doing this will not modify any behavior and is safe. If you specifically wanted the numpy scalar type, use `np.bool_` here.
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. Did you mean: 'bool_'?

To fix it, I have simply renamed np.bool to np.bool_.

[fuyb1992]

I got the same issue

[swell-d]

+1