records: refactoring fix
records: refactoring fix

* Fixes refactoring problem introduced when renaming '_files' to
  '_documents' in e24b55e8f1c497112d016888c825cbe276cf303c.

Signed-off-by: Lars Holm Nielsen <7eaffca9f7cd98839b5821d0d23e09ff764b82cd@cern.ch>
Reviewed-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

inveniosoftware/invenio,inveniosoftware/invenio,tiborsimko/invenio,tiborsimko/invenio