Fix query in extrusion example (#885)

ERROR: column t.tags does not exist

Author: yagagagaga

examples/extrusion/tileset.json

@@ -24,7 +24,7 @@
         {
           "minzoom": 12,
           "maxzoom": 20,
-          "sql": "SELECT id, tags || jsonb_build_object('building:height', (CASE WHEN tags ->> 'building:levels' ~ '^[0-9\\\\.]+$' THEN tags ->> 'building:levels' ELSE '1' END)::real * 3), geom FROM osm_ways WHERE tags ? 'building'"
+          "sql": "SELECT id, tags || jsonb_build_object('building:height', (CASE WHEN tags ->> 'building:levels' ~ '^[0-9\\\\.]+$' THEN tags ->> 'building:levels' ELSE '1' END)::real * 3) as tags, geom FROM osm_ways WHERE tags ? 'building'"
         }
       ]
     }