Update cubio.gd

a little wrong only.
Merge pull request #860 from Mavhod/patch-1

Update cubio.gd
SceneMainLoop -> SceneTree
-=-=-=-=-=-=-=-=-=-=-=-=-=-

*YOUR SOURCE MIGHT NOT WORK*
For mor information on fix:
https://github.com/okamstudio/godot/wiki/devel_scene_tree

Other stuff:
-Shower of bullets demo
-Fixes all around