Update dependencies (#886)

vendor/github.com/nlopes/slack/websocket_internals.go

@@ -18,6 +18,7 @@ type ConnectedEvent struct {
 // ConnectionErrorEvent contains information about a connection error
 type ConnectionErrorEvent struct {
 	Attempt  int
+	Backoff  time.Duration // how long we'll wait before the next attempt
 	ErrorObj error
 }
 
@@ -34,6 +35,7 @@ type ConnectingEvent struct {
 // DisconnectedEvent contains information about how we disconnected
 type DisconnectedEvent struct {
 	Intentional bool
+	Cause       error
 }
 
 // LatencyReport contains information about connection latency