Fix deprecated numpy dtype

[function2-llx]

Numpy has deprecated the aliases of builtin types like np.int since v1.20. When using a recent version of Numpy, exception will be raised when access the deprecated dtype. For example, #64 suggests to replace np.int with np.int_. There are also other examples found in the code:

pylidc/pylidc/Annotation.py

Line 1024 in 8c303c0

mask = np.zeros((ni,nj,nk), dtype=np.bool)

pylidc/pylidc/utils.py

Line 144 in 8c303c0

for c in find_contours(mask[slc(i)].astype(np.float), 0.5):