Fix order_by call in ExportManager
Fix order_by call in ExportManager

Previously it was just ordering the whole query by week__week, so the
users were coming in a random order. By changing the call to just use 1
order_by and giving it 2 arguments, we can get the results correctly
ordered for the export.

mysociety/manchester-survey,mysociety/manchester-survey,mysociety/manchester-survey,mysociety/manchester-survey,mysociety/manchester-survey