flops in Conv2D is wrong

[luuuyi]

First, nice work. But I found something wrong when calculating flops in torch.nn.Conv2d, in count_hooks.py file, the out_w = y.size(2) // m.stride[0] is wrong, it must be out_w = y.size(2). The same as out_h.
So the flops result is less than standard ones.

[luuuyi]

And y.size(2) should be H in NCH*W, in your code, it's W.

[Lyken17]

Thanks for the correction. PR merged.