Log Message:
net/ruby-slack-api: update to 1.6.0

1.5.0						2017/04/09

* fix attachments case
* chat.postMessage argument error only if both text and attachments are missing
* RealTime::Client has some information(self, team, channels, ...)
* @url was not, set rtm_start_response["url"] to @url to work properly

1.6.0						2017/07/12

* recognize multiple dot on endpoint