Use conversations.list
Use conversations.list

This patch makes the connect() method use the new converations.list
route instead of the now obsolete im.list one.

Without this patch, new apps built on top of Slack::RTM::Bot cannot
initiate. Previously created ones can still connect, until February 24th, 2021 [1]

[1]
https://api.slack.com/changelog//2020-01-deprecating-antecedents-to-the-conversations-api#prepare

Signed-off-by: Tomas Cohen Arazi <63ac9f6777fb741d62c33cd73a438a8ce82c7d4a@theke.io>

duck8823/Slack-RTM-Bot