`peer_assign()` fails with large files

I think... Some data files aren't being copied over to reviewer repo because they can't be retrieved. Fails with 

```
Unable to retrieve file 'data/[file_name]' from repo 'author_repo'.
```

Since these are all data files I suspect it might have to do with size. And I haven't yet looked into which step in `peer_assign()` is failing.