[GOBBLIN-1310] Update Slack invite link[]
[GOBBLIN-1310] Update Slack invite link[]

Closes #3148 from shirshanka/fixslackbadge

shirshanka/gobblin,linkedin/gobblin,jack-moseley/gobblin,jack-moseley/gobblin,shirshanka/gobblin,linkedin/gobblin,jack-moseley/gobblin,shirshanka/gobblin,arjun4084346/gobblin,abti/gobblin,shirshanka/gobblin,linkedin/gobblin,linkedin/gobblin,shirshanka/gobblin,abti/gobblin,arjun4084346/gobblin,jack-moseley/gobblin,abti/gobblin,arjun4084346/gobblin,arjun4084346/gobblin,jack-moseley/gobblin,linkedin/gobblin,arjun4084346/gobblin,linkedin/gobblin,abti/gobblin,abti/gobblin,abti/gobblin