``fast_forward()`` fails when there are multiple `fetch_info` objects returned from `remote.fetch()`

```
self = <elasticgit.manager.Workspace object at 0x1105d2510>, remote_name = 'origin'

    def fast_forward(self, remote_name='origin'):
        """
            Fetch & Merge in an upstream's commits.

            .. note::

                This assumes a single remote, chances are that will turn
                out to be incorrect soon.

            """
        remote = self.repo.remote(name=remote_name)
>       [fetch_info] = remote.fetch()
E       ValueError: too many values to unpack

../elastic-git/elasticgit/manager.py:587: ValueError
```