contributing page shows incorrect information.

[ByungJun25]

Documentation Is:

• Missing or needed
• Confusing
• Not Sure?

Please Explain in Detail...

Hello, Chart.js Team.

When I access a contributing.html page, the page shows that I can build with gulp. But according #7402 , the building system was changed to npm.

I checked a document file(link), it was already changed, I think it just wasn't shown correclty.

Example

[ByungJun25]

Hello, Chart.js Team.

I found a reason.

The document explain about version 2.9.3
But a code of master branch is for version 3.0.0

[etimberg]

@ByungJun25 for reference, https://www.chartjs.org/docs/master/ has the latest docs for the dev version