Update networks.py

[Roulbac]

Last Conv layer needs to have a stride of 2, just like in the article to keep the down-sampling factor as 2.
For the 70x70 PatchGAN, the last conv layer that brings the tensor to an Nx1x1x1 needs a kernel size of 4, a stride of 1 and no padding.
With padding, the output tensor is of shape Nx1x3x3 instead of Nx1x1x1 (for a 70x70 input).

Edit:
After more checks, it turns out that the added correction makes the receptive field of size 64x64 rather than 70x70. It is actually a convolutional implementation of the sliding window with stride 16 (because we have 4 downsamplings of factor 2, 2^4). With an input of size 80x80, the output is of size 2x2 corresponding to the 4 sliding windows with stride 16 each.

[junyanz]

I will keep the PatchGAN consistent with the Torch code. But you are free to use other discriminators in your experiments.