Dead link in CONTRIBUTING.md

[rgarrigue]

Hi there

On both suggested GIF recording tool, hasn't been maintained for 3 years, the other is a dead link.

Include screenshots and animated GIFs which help you demonstrate the steps or point out the part of git-pull-request which the suggestion is related to. You can use this tool to record GIFs on macOS and Windows, and this tool or this tool on Linux.

As an alternative I'm using Peek nowadays https://github.com/phw/peek