Updating a manufacturer name doesn't force a version bump of the manufacturer data

[peternewman]

http://rdm.openlighting.org/download?pids=manufacturers

[peternewman]

https://github.com/OpenLightingProject/rdm-app/blob/master/export.py#L162

[peternewman]

This will probably do the trick, needs testing though:

query.filter('name IN ', (timestamp_keys.PIDS, timestamp_keys.MANUFACTURERS)
query.order('-update_time')

The only minor downside, is a name change on a manufacturer who doesn't have any PIDs causes the timestamp to be updated, but it's probably not really worth trying to fix this edge case.