Lita does not reconnect after team_migration_started event

[shortdudey123]

Slack sometimes kicks all clients for a given team off to migrate them to another server. The lita-slack handler does not appear to try a reconnect after this occurs

[2016-06-04 05:01:28 UTC] DEBUG: team_migration_started event received from Slack and will be ignored.
[2016-06-04 05:01:28 UTC] INFO: Disconnected from Slack.
[2016-06-04 05:01:28 UTC] DEBUG: Closing connection to the Slack Real Time Messaging API.

https://api.slack.com/events/team_migration_started

(Might be related to #89 but since its not a nil event, i am creating a separate issue`