CSV contact importer attempts to coerce list to Unicode

```
Stacktrace (most recent call last):

(1 additional frame(s) were not displayed)
...
  File "celery/task/trace.py", line 420, in __protected_call__
    return self.run(*args, **kwargs)
  File "go/contacts/tasks.py", line 382, in import_upload_is_truth_contacts_file
    fields, has_header)
  File "go/contacts/tasks.py", line 330, in import_and_update_contacts
    for contact_dictionary in contact_dictionaries:
  File "go/contacts/parsers/base.py", line 230, i
 n parse_file
    for data_dictionary in data_dictionaries:
  File "go/contacts/parsers/csv_parser.py", line 45, in read_data_from_file
    for key, value in row.items()])
```