Fix label parent reference

Leaflet.FormBuilder.js

@@ -176,7 +176,7 @@ L.FormBuilder.Element = L.Class.extend({
 
     buildLabel: function () {
         if (this.options.label) {
-            this.label = L.DomUtil.create('label', '', this.builder.parentNode);
+            this.label = L.DomUtil.create('label', '', this.parentNode);
             this.label.innerHTML = this.options.label;
         }
     },

package.json

 {
   "name": "leaflet-formbuilder",
-  "version": "0.2.0",
+  "version": "0.2.1",
   "description": "Helpers to build forms in Leaflet",
   "main": "Leaflet.FormBuilder.js",
   "scripts": {