Added support for number values in json2xml conversion

I encountered a problem with the code originally where converting a JSON object like:

```{
  request_message : {
  request:'update',
  app_id:25,
  user_id:8
  }
}```

Would only output the following XML:

```<request_message request="update"></request_message>```

The modification I made supports numbers in the output. 

```<request_message request="update" app_id="25" user_id="8"></request_message>```