add a new type for the swagger model

add type of **{}** in SwaggerModelProperty.prototype.toSampleValue @ **lib/swgger.js** file

i think it may need to post some sub-obejct in the model
eg.
<pre>
{
  "name": "elvis",
  "children": {
    "abc1": {},
    "abc2": {},
   }
}
<pre>