Update mocha-json usage instructions

[MonkeyDo]

With mocha#4607 fixed and published in v9.1.0, users can output valid json using mocha's JSON reporter and the --reporter-option output={filename} option, provided version 9.1.0 or above is used.

This PR updates the readme to reflect this.

[IanMoroney]

@MonkeyDo , I ran into a similar issue as yourself where there were features that I needed from this project and looked like it wasn't being updated any time soon, so I took the initiative to fork the project myself and build the enhancements into it with a colleague.
I have also now taken this PR and added the contents into that repo so you can use them :)

https://github.com/phoenix-actions/test-reporting/
https://github.com/marketplace/actions/test-reporting

[jozefizso]

This PR look legit. I would say we may keep the mocha 9 instructions only.

The mocha 7 is for NodeJS 8 and mocha 9 for NodeJS 12+.

People using the mocha 7 can still get back to old instructions in the repo history.

[abenhamdine]

This PR look legit. I would say we may keep the mocha 9 instructions only.

The mocha 7 is for NodeJS 8 and mocha 9 for NodeJS 12+.

People using the mocha 7 can still get back to old instructions in the repo history.

mocha 10.2.0 has been published 1 year ago, I think it's time indeed to provide the "new" configuration --reporter-option output={filename}
I just set up a worfklow with mocha and I can confirm it works perfectly.