message: README: Fix Slack link
diff: @@ -75,4 +75,4 @@ at your option.
  Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.
  libhermit-rs is being developed on [GitHub](https://github.com/hermitcore/libhermit-rs).
  -Create your own fork, send us a pull request, and chat with us on [Slack](https://radiant-ridge-95061.herokuapp.com)
  +Create your own fork, send us a pull request, and chat with us on [Slack](https://matrix.osbyexample.com:3008)
  