Remove dangling commas

Currently when Studio generates layouts it leaves dangling commas:

• After the `type` declaration from the `document` property
• After the declaration of the `document` property

Example:

  <script>
    Polymer({
      is: 'nuxeo-process-edit-layout',
      behaviors: [Nuxeo.LayoutBehavior],
      properties: {        /**
         * @doctype Process
         */
        document: {
          type: Object,
        },
      }
    });
  </script>

This is visually very confusing and I have wasted hours (literally) troubleshooting problems only to realize I pasted a function inside the properties block.