text: Title: Can not add graph for dataparallel model
  Body: Hi there, I get a  `KeyError: '322'` when I try to `add_graph` for data parallel model on multiple GPU. Here is a mini-example which can reproduce the error:
  
  So what should I do for this error?
  
  ```
  import torch
  import torchvision.models as models
  from tensorboardX import SummaryWriter
  
  device = 'cuda'
  
  net = torch.nn.DataParallel(models.__dict__['resnet50']().to(device))
  dump_input = torch.rand((10, 3, 224, 224), device=device)
  SummaryWriter('./tmp').add_graph(net, dump_input, verbose=False)
  ```
  