Functions in fft_utils.py does not match version of torch>=1.8

[yangpuPKU]

Thanks for this repository.

In the file activemri/experimental/cvpr19_models/models/fft_utils.py, the functions of torch.fft, torch.ifft and torch.rfft of torch<=1.7 are used for the implementation of the Fast Fourier Transform. However, these functions are dropped in the new version of torch>=1.8 and replaced with torch.fft.fft, torch.fft.ifft and torch.fft.rfft. What's more, the packages this code depends on include fastmri which depends on torch>=1.8. The above problems will lead to a bug when running the intro notebook

It would be nice to update fft_utils.py to the new version.

Thanks,
Pu Yang