Slack invite link broken in README

[MCBoarder289]

When trying to join the community Slack linked in the README, you receive a page with the following message:

This link is no longer active
To join this workspace, you’ll need to ask the person who originally invited you for a new link.

How to reproduce the bug

1. Go to 'README.md'
2. Click the "Join our community's Slack" link
3. See error

Expected results

Get an invite to the Slack community

Actual results

Get an inactive link error message

Environment

(please complete the following information):

• Chrome 99.0.4844.84
• superset version: master branch
• python version: N/A
• node.js version: N/A
• any feature flags active: no

Checklist

Make sure to follow these steps before submitting your issue - thank you!

• I have checked the superset logs for python stacktraces and included it here as text if there are any.
• I have reproduced the issue with at least the latest released version of superset.
• I have checked the issue tracker for the same issue and I haven't found one similar.

Additional context

Seems similar to this older issue: #8613

[srinify]

Thanks @MCBoarder289 for the catch! I will fix this ASAP