LRN for new pytorch version

[chingjunehao]

Thanks for your work, helped me a lot, but I did modify some lines of code to adapt the latest version of Pytorch. I use this is to replace the legacy module. from torch.nn.modules import CrossMapLRN2d as SpatialCrossMapLRNOld and the code in the below link, https://github.com/jiecaoyu/pytorch_imagenet/blob/master/networks/model_list/alexnet.py to replace the LRN function. Which works fine.