Update index.md with new slack link

Author: chrisrichardson

community/index.md

@@ -25,7 +25,7 @@ More advice on how to post a good question is
 Discussions about FEniCS and its development take place on the [FEniCS
 Slack channels](https://fenicsproject.slack.com/). You can join the
 Slack community by
-[entering your email address at this link](https://join.slack.com/t/fenicsproject/shared_invite/zt-1lraknsp1-6_3Js5kueDIyWgF192d3nA).
+[entering your email address at this link](https://join.slack.com/t/fenicsproject/shared_invite/zt-2wa76d0xw-ecfxcPj25K8pc7q7~1AK8g).
 
 ## Reporting bugs