Blender exporter: Fix reference to missing constant

This made exporting scenes with light not work.

utils/exporters/blender/addons/io_three/exporter/api/object.py

@@ -314,7 +314,7 @@ def node_type(obj):
             POINT: constants.POINT_LIGHT,
             SUN: constants.DIRECTIONAL_LIGHT,
             SPOT: constants.SPOT_LIGHT,
-            AREA: constants.AREA_LIGHT,
+            AREA: constants.RECT_AREA_LIGHT,
             HEMI: constants.HEMISPHERE_LIGHT
         },
         CAMERA: {