Use cupy backend but complicts with planer/io.py

[tangjie77wd]

I have successfully run the cellpose demo without cupy which means i downloaded cellpose.onnx and segmented cell.png with it successully according to cellpose-planer.py.
However,when i set cupy as backend:
import cupy planer.core(cupy)
Error informations occurs because read_onnx function in planer/io.py using numpy everywhere ( just like the following shows ) complicts with demo after i set cupy as backend in demo.
v_inv=1/np.sqrt(...)