Fix duration

edit-mode/function/ganttEvent.js

@@ -56,14 +56,14 @@ gantt.attachEvent("onBeforeTaskUpdate", function(id,new_item){
     let link = task.$target;
     // link.length > 0 -> successor
     new_item['progress'] = progress;
-    new_item['duration'] = new_item['duration'] + (link.length == 0 ? 1 : 1);
+    new_item['duration'] = new_item['duration'] + (link.length == 0 ? 0 : 1);
     new_item['end_date'] = gantt.calculateEndDate({
       start_date: new_item['start_date'],
       duration: new_item['duration']
     })
     new_item['end_date'].setHours(23,59,59);
     if (editDurationTriggered) {
-      let tempDuration = new_item['duration'] - (link.length == 0 ? 1 : 1);
+      let tempDuration = new_item['duration'] - 1;
       new_item['end_date'] = gantt.calculateEndDate({
         start_date: new_item['start_date'],
         duration: tempDuration