change TriggerKind format for external event.

events/external.go

@@ -12,7 +12,7 @@ func (e ExternalEvent) EventDescription() string {
 }
 
 func (e ExternalEvent) TriggerKind() string {
-	return fmt.Sprintf("External[%s]", e.Kind)
+	return fmt.Sprintf("External:%s", e.Kind)
 }
 
 func (e ExternalEvent) TriggerValue(key string) (string, bool) {