ES needs to be updated when stuff is deleted.

Currently a fast-forward assumes only new data is added, removed stuff does not result in an updated ES index.
Shouldn't this be handle by `ws.pull()` [here](https://github.com/universalcore/elastic-git/pull/38/files#diff-0e3a516569d221185445e1cb7593f962R662):
```python
if len(self.repo.remotes) > 1 and any(changes.iter_change_type('D')):
    # reindex everything
    ...
```