text: Title: AttributeError: 'torch._C.Node' object has no attribute 'schema'
  Body: I use the tool to try to prue my model such as (https://github.com/microsoft/nni/blob/dab51f799f77aa72c18774faffaedf8d0ee2c977/examples/model_compress/pruning/admm_pruning_torch.py)
  I only change the model(with restnet) and the dataloader:
  But now there is some problem when I use ModelSpeedup
    File "<ipython-input-7-25297990bbbb>", line 1, in <module>
      ModelSpeedup(model, torch.randn([1, 2, 224, 224]).to(device), masks).speedup_model()
    File "D:\anaconda3\lib\site-packages\nni\compression\pytorch\speedup\compressor.py", line 543, in speedup_model
      self.infer_modules_masks()
    File "D:\anaconda3\lib\site-packages\nni\compression\pytorch\speedup\compressor.py", line 380, in infer_modules_masks
      self.update_direct_sparsity(curnode)
    File "D:\anaconda3\lib\site-packages\nni\compression\pytorch\speedup\compressor.py", line 228, in update_direct_sparsity
      func = jit_to_python_function(node, self)
    File "D:\anaconda3\lib\site-packages\nni\compression\pytorch\speedup\jit_translate.py", line 554, in jit_to_python_function
      return trans_func_dict[node.op_type](node, speedup)
    File "D:\anaconda3\lib\site-packages\nni\compression\pytorch\speedup\jit_translate.py", line 488, in generate_aten_to_python
      schema = c_node.schema()
  AttributeError: 'torch._C.Node' object has no attribute 'schema'