kill task after hangup or refer

lib/tasks/cognigy/index.js

@@ -223,12 +223,14 @@ class Cognigy extends Task {
             this.performAction({cognigyResult: 'hangup Succeeded'});
             this.reportedFinalAction = true;
             this.notifyTaskDone();
+            this.kill(cs);
             return;
           case 'refer':
             await this._makeReferTask(evt.data.number);
             this.performAction({cognigyResult: 'refer succeeded'});
             this.reportedFinalAction = true;
             this.notifyTaskDone();
+            this.kill(cs);
             return;
           default:
             break;