Fix broken option in jquery.wikibase.linkitem.js

This mistake was introduced in Ibae5bfc. It makes the client widget
unusable. Please backport this fix since it is on the live site as
far as I can tell.

Change-Id: Ia12eda93408a5d4a0f0efa2dcc45b3fbbdd51446
Merge "Fix broken option in jquery.wikibase.linkitem.js"