Set verify_mode explicitly
Set verify_mode explicitly

websocket-client-simple have deprecated and insecure defaults of
SSLContext.
https://github.com/shokai/websocket-client-simple/blob/v0.3.0/lib/websocket-client-simple/client.rb

kinoppyd/ruboty-slack_rtm,rosylilly/ruboty-slack_rtm,YasuhiroKinoshita/ruboty-slack_rtm,tsuwatch/ruboty-slack_rtm