Add function return type

# source

``` python
class Xxx():
    def get_xxx(self, arg: str) -> str:
        pass
```

# actual

## Xxx
```python 
Xxx()
```
---

**Methods:**

### .get_xxx
```python
.get_xxx(
   arg: str
)
```



# expected

## Xxx
```python 
Xxx()
```
---

**Methods:**

### .get_xxx
```python
.get_xxx(
   arg: str
) -> str
```
