Replace expired slack invite link
Closes from shirshanka/slack-readme
@@ -39,7 +39,7 @@ The distribution will be created in build/gobblin-distribution/distributions dir
* [Gobblin documentation](https://gobblin.apache.org/docs/)
* [Getting started guide](https://gobblin.apache.org/docs/Getting-Started/)
* [Gobblin architecture](https://gobblin.apache.org/docs/Gobblin-Architecture/)
- * Community Slack: [Sign up](https://join.slack.com/t/apache-gobblin/shared_invite/zt-hkwu51id-aVxL3bvtLdi778YHFV1b6A) or [login with existing account](https://apache-gobblin.slack.com) to `apache-gobblin` space on Slack
+ * Community Slack: [Get your invite](https://communityinviter.com/apps/apache-gobblin/apache-gobblin)
* [List of companies known to use Gobblin](https://gobblin.apache.org/docs/Powered-By/)
* [Sample project](https://github.com/apache/incubator-gobblin/tree/master/gobblin-example)
* [How to build Gobblin from source code](https://gobblin.apache.org/docs/user-guide/Building-Gobblin/)
