`CONTRIBUTING.md`: references broken jsfiddle

[ppena-LiveData]

Description:

The Raising issues section of CONTRIBUTING.md references this jsfiddle that no longer works:

Even better, you could create a failing test case using this jsfiddle as a base.

The CONTRIBUTING.md doc also mentions https://jsfiddle.net/evschris/wxc00vup/ and https://ractive.js.org/playground/. What is the preferred base for showing issue reproductions?

[evs-chris]

The playground is preferred for issue reproductions.