Intellisense is wrong with staticmethod

https://github.com/Microsoft/vscode-python/issues/182


![image](https://user-images.githubusercontent.com/12820357/46623825-c49fe400-cae3-11e8-89ae-e25ec914b51d.png)

Intellisense in `foo` method is wrong, `formmater`. need show `str`'s method, like `format()`, but it will show `Test`'s method, like `foo()`
