Feature/jp 6199 use json5 instead of comment json

[rahulpshah]

References

Fixes #6199

Code changes

Use json5 and update package.json

[jupyterlab-dev-mode]

Thanks for making a pull request to JupyterLab!

To try out this branch on binder, follow this link:

[blink1073]

Thanks, @rahulnexus! Can you please try running jlpm at the repo root and then committing the change? It looks like you have a different version of yarn that is causing the huge line diff.

[jasongrout]

Thanks!