Monitor Process Model raises deprecation warnings (np.float)

[mathisrichter]

The unit tests for the Monitor Process lead to deprecation warnings:

lava-nc\lava\src\lava\proc\monitor\models.py:23: DeprecationWarning: `np.float` is a deprecated alias for the builtin `float`. To silence this warning, use `float` by itself. Doing this will not modify any behavior and is safe. If you specifically wanted the numpy scalar type, use `np.float64` here.
Deprecated in NumPy 1.20; for more details and guidance: https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations
  np.float,
lava-nc\lava\src\lava\proc\monitor\models.py:26: DeprecationWarning: `np.float` is a deprecated alias for the builtin `float`. To silence this warning, use `float` by itself. Doing this will not modify any behavior and is safe. If you specifically wanted the numpy scalar type, use `np.float64` here.
Deprecated in NumPy 1.20; for more details and guidance: https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations
  np.float,

Suggested fix: Replace any occurence of np.float with float (models.py, lines 23 and 26)

[elvinhajizada]

@mathisrichter will do the suggested fix