updating test_nearest_neighbor_distances()

[jGaboardi]

This PR updates test_nearest_neighbor_distances() to account for a VisibleDeprecationWarning in numpy.

spaghetti/tests/test_api_network.py::TestNetworkPointPattern::test_nearest_neighbor_distances
spaghetti/tests/test_dev_network.py::TestNetworkPointPattern::test_nearest_neighbor_distances
  /Users/user/spaghetti/spaghetti/tests/network_unittest_classes.py:638: VisibleDeprecationWarning: Creating an ndarray from ragged nested sequences (which is a list-or-tuple of lists-or-tuples-or ndarrays with different lengths or shapes) is deprecated. If you meant to do this, you must specify 'dtype=object' when creating the ndarray
    nndv1 = numpy.array(list(nnd2.values()))[:, 1].astype(float)

spaghetti/tests/test_api_network.py::TestNetworkPointPattern::test_nearest_neighbor_distances
spaghetti/tests/test_dev_network.py::TestNetworkPointPattern::test_nearest_neighbor_distances
  /Users/user/spaghetti/spaghetti/tests/network_unittest_classes.py:638: VisibleDeprecationWarning: Creating an ndarray from ragged nested sequences (which is a list-or-tuple of lists-or-tuples-or ndarrays with different lengths or shapes) is deprecated. If you meant to do this, you must specify 'dtype=object' when creating the ndarray
    nndv2 = numpy.array(list(nnd2.values()))[:, 1].astype(float)