fixes issue when using the same instance of json2xml

Author: c4milo

lib/json2xml.js

@@ -1,5 +1,5 @@
-var xml = '';
-module.exports = function toXml(json) {
+module.exports = function toXml(json, xml) {
+    var xml = xml || '';
     if (json instanceof Buffer) {
         json = json.toString();
     }
@@ -26,12 +26,12 @@ module.exports = function toXml(json) {
             var l = elems.length;
             for (var j = 0; j < l; j++) {
                 xml += '<' + key + '>';
-                toXml(elems[j]);
+                xml = toXml(elems[j], xml);
                 xml += '</' + key + '>';
             }
         } else if (typeof(obj[key]) == 'object') {
             xml += '<' + key + '>';
-            toXml(obj[key]);
+            xml = toXml(obj[key], xml);
             xml += '</' + key + '>';
         } else if (typeof(obj[key]) == 'string') {
             if (key == '$t') {