add new invite link without expiration date (#165)

merging because link doesn't work rn and this is not a code change.

README.md

@@ -11,7 +11,7 @@ resulting in a sum that is greater than its individual parts.
 
 You can read more about Nebula [here](https://medium.com/p/884110a5579).
 
-You can also join the NebulaOSS Slack group [here](https://join.slack.com/t/nebulaoss/shared_invite/enQtODY1OTg4MDkwMDM0LWI0ZmI5NDMxOTI2OGM5NzVhYjQxOTZlY2U1NWJlMDhkODJkYThhN2VkMTJjMGEzZjM5Y2YxMDhmYWMxNWE3YmY)
+You can also join the NebulaOSS Slack group [here](https://join.slack.com/t/nebulaoss/shared_invite/enQtOTA5MDI4NDg3MTg4LTkwY2EwNTI4NzQyMzc0M2ZlODBjNWI3NTY1MzhiOThiMmZlZjVkMTI0NGY4YTMyNjUwMWEyNzNkZTJmYzQxOGU)
 
 ## Technical Overview