np.int is deprecated in numpy>=1.20 - use np.int32 instead

[mxkrn]

Fix in response to the warnings that I currently get when using pretty_midi==0.2.9 and numpy>=1.20, here's the original warning message:

lib/python3.9/site-packages/pretty_midi/pretty_midi.py:295: 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
    current_instrument = np.zeros(16, dtype=np.int)

[craffel]

Thanks!

[LiteApplication]

if np.int is an alias for the builtin int, why not use directly np.zeros(16, dtype=int) instead of np.int32 ?