Fixed execution listener export (reported here:...

Fixed execution listener export (reported here: https://forums.activiti.org/content/execution-listener-not-getting-exported)

modules/activiti-json-converter/src/main/java/org/activiti/editor/language/json/converter/BpmnJsonConverterUtil.java

@@ -17,7 +17,6 @@ import java.util.Collection;
 import java.util.List;
 
 import org.activiti.bpmn.model.ActivitiListener;
-import org.activiti.bpmn.model.Activity;
 import org.activiti.bpmn.model.BaseElement;
 import org.activiti.bpmn.model.BooleanDataObject;
 import org.activiti.bpmn.model.BpmnModel;
@@ -25,6 +24,7 @@ import org.activiti.bpmn.model.DateDataObject;
 import org.activiti.bpmn.model.DoubleDataObject;
 import org.activiti.bpmn.model.EventListener;
 import org.activiti.bpmn.model.FieldExtension;
+import org.activiti.bpmn.model.FlowElement;
 import org.activiti.bpmn.model.ImplementationType;
 import org.activiti.bpmn.model.IntegerDataObject;
 import org.activiti.bpmn.model.ItemDefinition;
@@ -350,8 +350,8 @@ public class BpmnJsonConverterUtil implements EditorJsonConstants, StencilConsta
           } else {
             ((UserTask) element).getExecutionListeners().add(listener);
           }
-        } else if (element instanceof Activity) {
-          ((Activity) element).getExecutionListeners().add(listener);
+        }  else if (element instanceof FlowElement) {
+          ((FlowElement) element).getExecutionListeners().add(listener);
         }
       }
     }