A suggestion for compGCN example in DGL

Recently, I tried the compGCN example in DGL, and I found something that may be improved.

  1. This line should be changed into train_loss.append(tr_loss.item()) for the efficiency of GPU.
  2. For users whose pytorch version >= 1.8, this line should be changed into return th.fft.irfftn(th.conj(th.fft.rfftn(a, (-1))) * th.fft.rfftn(b, (-1)), (-1)), as the Fourier transformation APIs of pytorch have changes.

Hi,

Thanks for the suggestion. Would you like to submit a PR for this problem?

Yes, I would like to.