update ctable ref

Ctable currently broken on prod after jsonobject switch. Bug was already fixed but not deployed: https://github.com/dimagi/ctable/commit/79dfa017cb2f2a8e0d5fcd12a145d1cbed6ef69f

The reason it broke now is that jsonobject handles default values for ListProperty differently to how couchdbkit does. Couchdbkit clones the default list before returning it which jsonobject doesn't. @dannyroberts not sure if this is good or not but I guess its more consistent with what happens when non-default values.

[Relevant line in Coucdbkit](https://github.com/benoitc/couchdbkit/blob/master/couchdbkit/schema/properties.py#L529)
[Relevant line in jsonobject](https://github.com/dannyroberts/jsonobject/blob/master/jsonobject/base.py#L19)