Replace IRC with Slack

Author: rfscholte

README.md

@@ -88,7 +88,7 @@ Additional Resources
 + [General GitHub documentation](https://help.github.com/)
 + [GitHub pull request documentation](https://help.github.com/send-pull-requests/)
 + [Apache Maven Twitter Account](https://twitter.com/ASFMavenProject)
-+ #Maven IRC channel on freenode.org
++ `#Maven channel` on [ASFs Slack](https://the-asf.slack.com)
 
 [jira]: https://issues.apache.org/jira/projects/MJAVADOC/
 [license]: https://www.apache.org/licenses/LICENSE-2.0