Obstacles don't scale if the viewport changes vertically

[ryanwarsaw]

This isn't exactly a common problem, but if the user shrinks their viewport the pipes begin to overlap and create a "wall" effect. These should re-scale appropriately when viewport changes.

[ryanwarsaw]

When I refactored the obstacle code and implemented the ObstacleManager I made note to split out the scaling code, so there is now a handy rescale() method available that'll do exactly this. Just need to implement an event listener that'll call the method, an update the DOM.