Failed to open *.plotly.json file

[jonmmease]

Issue

Opening a *.plotly.json file failes

Versions

@jupyterlab/plotly-extension: 0.17.1
JupyterLab 0.34.0

To reproduce

Create a file named fig.plotly.json with contents:

{"data": [{"y": [2, 3, 1]}]}

Double click file in JupyterLab to open. The following error is displayed

Chrome developer console error:

[jonmmease]

Fixed by #159