Wrap line after variable annotation, if possible.

Using yapf 0.29.0 with google style, I'm getting:

```python
dkfjghdfkjgdhfkgdfkjgh: Union[Slsdfjhdslfkj,
Gsdklfjdklsfjdsl] = (sdfkljdsklfjdsklfjsdklfj)
```

This is just my opinion of course, but I think it would look nicer as:

```python
dkfjghdfkjgdhfkgdfkjgh: Union[Slsdfjhdslfkj, Gsdklfjdklsfjdsl] = (
sdfkljdsklfjdsklfjsdklfj)
```