[Bug Report] dgl_gcn example not working per readme

**Link to the notebook**
Replicating the readme files https://github.com/aws/amazon-sagemaker-examples/tree/main/sagemaker-python-sdk/dgl_gcn

**Describe the bug**
After creation of the DGL_py36_pytorch1.2 environment, with pytorch backend, selecting the environment does not work (broken link symbol, and says the notebook server is not communicating).

**To reproduce**
```
# Clone python3 environment
conda create --name DGL_py36_pytorch1.2 --clone python3

# Install PyTorch and DGL
conda install --name DGL_py36_pytorch1.2 pytorch=1.2 torchvision -c pytorch
conda install --name DGL_py36_pytorch1.2 -c dglteam dgl-cuda10.0
```
then, open a notebook, select "conda_dgl_py36_pytorch1.2" as the kernel. This should replicate the error.

**Logs**
If applicable, add logs to help explain your problem.
You may also attach an `.ipynb` file to this issue if it includes relevant logs or output.