Update NodeEditor.cs

I initially found out about this through
https://docs.unity3d.com/ScriptReference/Editor.html 
specifically these two comments:

```csharp
// Update the serializedProperty - always do this in the beginning of OnInspectorGUI.
        serializedObject.Update ();
...
// Apply changes to the serializedProperty - always do this in the end of OnInspectorGUI.
        serializedObject.ApplyModifiedProperties ();
```

I'm assuming, although I don't know for sure, that since OnBodyGUI displays the serialize objects in the custom inspector, that it must follow the same rules as well. Either way these lines of code solve for me the glitch: pressing undo while typing and getting a disconnect between the node and the inspector.

Scripts/Editor/NodeEditor.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using UnityEditor;
@@ -43,6 +43,10 @@ public class NodeEditor : XNodeEditor.Internal.NodeEditorBase<NodeEditor, NodeEd
 
         /// <summary> Draws standard field editors for all public fields </summary>
         public virtual void OnBodyGUI() {
+            // Unity specifically requires this to save/update any serial object.
+            // serializedObject.Update(); must go at the start of an inspector gui, and
+            // serializedObject.ApplyModifiedProperties(); goes at the end.
+            serializedObject.Update();
             string[] excludes = { "m_Script", "graph", "position", "ports" };
             portPositions = new Dictionary<XNode.NodePort, Vector2>();
 
@@ -54,6 +58,7 @@ public class NodeEditor : XNodeEditor.Internal.NodeEditorBase<NodeEditor, NodeEd
                 if (excludes.Contains(iterator.name)) continue;
                 NodeEditorGUILayout.PropertyField(iterator, true);
             }
+            serializedObject.ApplyModifiedProperties();
         }
 
         public virtual int GetWidth() {
@@ -93,4 +98,5 @@ public class CustomNodeEditorAttribute : Attribute,
             }
         }
     }
-}
+
+}