stock_movements helper fix for stock_transfer

Fixes pretty_originator exception for stock movement created by stock transfer between 2 locations.

Versions: rails: 4.0.*, spree: 2.1.4beta (2.1.3beta)

Steps to reproduce:

1) admin/stock_transfers/new
  create a new transfer between two locations

2) admin/stock_locations

3) admin/stock_locations/{location_id}/stock_movements
 raises "undefined method order" exception


Fix:

  return originator.number as in previous version