Legacy autograd function with non-static forward method is deprecate

[Abbas009]

In running the Tversky loss following error Occurred.
"Legacy autograd function with non-static forward method is deprecated. "
RuntimeError: Legacy autograd function with non-static forward method is deprecated. Please use new-style autograd function with static forward method. (Example: https://pytorch.org/docs/stable/autograd.html#torch.autograd.Function)
Pytorch==1.7.0