Add update_user to the long import list

Without update_user in prr.py I saw the following:

```
$ heroku run python db_users.py
Running `python db_users.py` attached to terminal... up, run.4561
Traceback (most recent call last):
  File "db_users.py", line 4, in <module>
    set_directory_fields()
  File "/app/public_records_portal/prr.py", line 283, in set_directory_fields
    update_user(user = user, is_staff = False)
NameError: global name 'update_user' is not defined
$
```