DraggableSubsets example accepts incorrect responses

[dlglin]

Originally reported at https://webwork.maa.org/moodle/mod/forum/discuss.php?d=8308

The DraggableSubsets example should have OrderedSubsets => 1.

[drgrice1]

This will be fixed with pstaabp/pg#21 (a pull request to openwebwork/pg#811 where the actual sample problems currently reside).