Editor: draggable.attributes.src missing in xmlQuestionConfig.js (easy to fix)

This will give an error message in the editor:

<draggable identifier="d1" src="[attachurl:dd_plus_P.png]" />

"An unknown parameter 'src' was found in an item of type 'draggable'"

In xmlQuestionConfig.js, the src attribute is indeed not defined (starting at line 1174) in draggable.attributes:

"draggable": {
      "content": 1,
      "attributes": {
        "id": {
          "title": "Identifier",
          "description": "A unique name for this item."
        },
        "identifier": {
          "alias_of": "id"
        },
        "class": {
          "title": "class",
          "description": "The CSS class used to style this draggable."
        }
      },
      "valid_children": [],
      "max_children": 0,
      "icon": {
        "image": "icons/draggable_icon.png"
      },
      "atts_in_title": ["id"]
    },
    "default": {
      "alias_of": "startstate"
    }