Roadmap link does not work on the CONTRIBUTING.md file

[JAroyan]

Hi,
on the CONTRIBUTING.md file the link "Roadmap" does not work.
https://github.com/microsoft/LightGBM/blob/master/CONTRIBUTING.md

[jameslamb]

Thanks very much for reporting this! We'll remove that link.

I believe it's left over from a brief period where Microsoft had assigned a Product Manager to LightGBM. We don't maintain a public roadmap (with sequencing, priority, or due dates)... at this point, the work is very self-directed.

You can see #2302 for a list of all feature requests.