Unexpected space after keyword argument

`yapf --style=pep8` formats the following code:

```python
class ConjectureRunner(object):

def _(
self, test_function, settings=None,
):
self.settings = ConjectureData(
draw_bytes=lambda data, n, distribution:
distribution(self.random, n)
)
```

as the following output:

```python
class ConjectureRunner(object):
def _(
self,
test_function,
settings=None, ):
self.settings = ConjectureData(
draw_bytes=
lambda data, n, distribution: distribution(self.random, n))
```

The space after "settings=None," seems to be incorrect according to pep8 (both my interpretation of it and the pycodestyle checker's claim).

I've verified this both with yapf 0.16.1 and the current version in da3697c012016665b9fc537ce694bbc5bc7101dd