Douglas Lehr

Update onnx_graph_to_caffe2_net call

1

The tutorial [CorrectnessVerificationAndPerformanceComparison.ipynb](https://github.com/onnx/tutorials/blob/master/tutorials/CorrectnessVerificationAndPerformanceComparison.ipynb) has an old call to `Caffe2Backend.onnx_graph_to_caffe2_net` which references `onnx_model.graph` instead of just the model `onnx_model` Resulting in the error ``` init_net, predict_net = Caffe2Backend.onnx_graph_to_caffe2_net(onnx_model.graph, device="CPU") File "/opt/DL/pytorch/lib/python2.7/site-packages/caffe2/python/onnx/backend.py",...