Fixed face normals computation
Fixed face normals computation

hirosuke999/three.dart,james-storey/three.dart,james-storey/three.dart,threeDart/three.dart,brason/three.dart,threeDart/three.dart,hirosuke999/three.dart,threeDart/three.dart,hirosuke999/three.dart,brason/three.dart,brason/three.dart