chore: updated Slack URL, old link expired (#12737)

README.md

@@ -26,7 +26,7 @@ Superset
 [![PyPI version](https://badge.fury.io/py/apache-superset.svg)](https://badge.fury.io/py/apache-superset)
 [![Coverage Status](https://codecov.io/github/apache/superset/coverage.svg?branch=master)](https://codecov.io/github/apache/superset)
 [![PyPI](https://img.shields.io/pypi/pyversions/apache-superset.svg?maxAge=2592000)](https://pypi.python.org/pypi/apache-superset)
-[![Get on Slack](https://img.shields.io/badge/slack-join-orange.svg)](https://join.slack.com/t/apache-superset/shared_invite/zt-g8lpruog-HeqpgYrwdfrD5OYhlU7hPQ)
+[![Get on Slack](https://img.shields.io/badge/slack-join-orange.svg)](https://join.slack.com/t/apache-superset/shared_invite/zt-l5f5e0av-fyYu8tlfdqbMdz_sPLwUqQ)
 [![Documentation](https://img.shields.io/badge/docs-apache.org-blue.svg)](https://superset.apache.org)
 [![Dependencies Status](https://david-dm.org/apache/superset/status.svg?path=superset-frontend)](https://david-dm.org/apache/superset?path=superset-frontend)
 
@@ -137,7 +137,7 @@ Want to add support for your datastore or data engine? Read more [here](https://
 ## Get Involved
 
 * Ask and answer questions on [StackOverflow](https://stackoverflow.com/questions/tagged/apache-superset) using the **apache-superset** tag
-* [Join our community's Slack](https://join.slack.com/t/apache-superset/shared_invite/zt-g8lpruog-HeqpgYrwdfrD5OYhlU7hPQ)
+* [Join our community's Slack](https://join.slack.com/t/apache-superset/shared_invite/zt-l5f5e0av-fyYu8tlfdqbMdz_sPLwUqQ)
   and please read our [Slack Community Guidelines](CODE_OF_CONDUCT.md#slack-community-guidelines)
 * [Join our dev@superset.apache.org Mailing list](https://lists.apache.org/list.html?dev@superset.apache.org)