Change where clause in unique_key example

The where clause in the unique_key example referred to event_time, but event_time isn't in the select statement. So this should be updated to date_day.

website/docs/docs/build/incremental-models.md

@@ -142,7 +142,7 @@ from {{ ref('app_data_events') }}
 
   -- this filter will only be applied on an incremental run
   -- (uses >= to include records arriving later on the same day as the last run of this model)
-  where date_day >= (select coalesce(max(event_time), '1900-01-01') from {{ this }})
+  where date_day >= (select coalesce(max(date_day), '1900-01-01') from {{ this }})
 
 {% endif %}