Dependency will cause jupyter notebook to crash

In case of anyone who bump into this problem.
```
/Users/tnlin/anaconda3/lib/python3.6/site-packages/notebook/base/zmqhandlers.py:284: RuntimeWarning: coroutine 'WebSocketHandler.get' was never awaited
super(AuthenticatedZMQStreamHandler, self).get(*args, **kwargs)
[W 11:53:18.115 NotebookApp] Replacing stale connection: e1c43480-dd1f-4837-b57d-197e2e20fdb9:24e703ae04c9484c896ecbd5c506b419
```

My jupyter notebook fail to connect the kernel after install the dependency `tornado-6.0.3`
I solve the issue by downgrading it: `pip install tornado==5.1.1`

For for details, see: https://github.com/jupyter/notebook/issues/4437

Here are my dependencies:
```
Python 3.6.9
jupyter==1.0.0
jupyter-client==5.2.3
jupyter-console==6.0.0
jupyter-contrib-core==0.3.3
jupyter-contrib-nbextensions==0.4.0
jupyter-core==4.4.0
jupyter-highlight-selected-word==0.1.0
jupyter-latex-envs==1.4.6
jupyter-nbextensions-configurator==0.4.0
jupyterlab==0.32.1
jupyterlab-launcher==0.10.5
jupyterthemes==0.18.9
notebook==5.5.0
```

Start by reproducing the kernel connection failure with the listed Python, Jupyter, notebook, and tornado versions, then compare the dependency requirements with the referenced Jupyter issue. Done means establishing a compatible dependency set or documenting the supported versions so the kernel connects without the reported warning.

Written by the indexing model from the issue text.