Fix aspect-ratio of current camera #44

Currently the aspect-ratio of the current camera of the scene is automatically set only when resizing the canvas and on the initial render via a ResizeObserver. This causes unexpected behavior when setting a <T.Camera /> to current camera, where it defaults the aspect-ratio to 1 / 1.

In react-three-fiber they update the camera whenever it is set via contrext and bail out of automatic aspect-ratio update when the manual-property is set to true.