Not escape nested json value

```java
// expected
// {
//      "parent": {
//          "childKey": "childValue"
//      }
// }
RequestParams requestParams  = new RequestParams();
requestParams.setUseJsonStreamer(true);
JSONObject jsonObject = new JSONObject();
jsonObject.put("childKey", "childValue");
requestParams.put("parent", jsonObject);
HttpEntity httpEntity = requestParams.getEntity(null);
OutputStream outputStream  = new ByteArrayOutputStream();
httpEntity.writeTo(outputStream);
String actual = outputStream.toString();
// actual
// {
//      "parent": "{
//          \"childKey\": \"childValue\"
//      }"
// }
```