plus_mons 出現 AttributeError: 'Stock' object has no attribute '_FetchData__raw_data'

當我嘗試增加月份時，使用 plus_mons 出現了下列錯誤

```
  File "../A/B.py", line 33, in queryPrice
    stock.plus_mons(1)
  File "/Library/Python/2.7/site-packages/grs-0.6.2-py2.7.egg/grs/fetch_data.py", line 121, in plus_mons
    oldraw = list(self.__raw_data)
AttributeError: 'Stock' object has no attribute '_FetchData__raw_data'
```
