docs: update slack invite-link in readme (mrdoob#22012)

Author: usefulthink

README.md

@@ -16,7 +16,7 @@ The aim of the project is to create an easy to use, lightweight, cross-browser,
 [Migrating](https://github.com/mrdoob/three.js/wiki/Migration-Guide) —
 [Questions](http://stackoverflow.com/questions/tagged/three.js) —
 [Forum](https://discourse.threejs.org/) —
-[Slack](https://join.slack.com/t/threejs/shared_invite/enQtMzYxMzczODM2OTgxLTQ1YmY4YTQxOTFjNDAzYmQ4NjU2YzRhNzliY2RiNDEyYjU2MjhhODgyYWQ5Y2MyZTU3MWNkOGVmOGRhOTQzYTk) —
+[Slack](https://join.slack.com/t/threejs/shared_invite/zt-rnuegz5e-FQpc6YboDVW~5idlp7GfDw) —
 [Discord](https://discordapp.com/invite/HF4UdyF)
 
 ### Usage ###