Unable to update line item properties.

[gavinballard]

Our documentation currently suggests that you could use updateItem or updateItemById to change the line item properties of an existing line item, but that's not actually possible with the Shopify Ajax API.

We need to update the documentation to reflect this and suggest the workaround of removing the line item, then re-adding it.

[austinhutchison]

My experience here is that updateItem will work with a properties parameter, but updateItemById does not. Also, it will overwrite existing line item properties.