prevent `mouseover` callback from firing after a `mouseout`

In my testing, I found that if you have an interactive element at the edge of the canvas, hover over it, and then move the mouse off the canvas, the `mouseover` callback would get called shortly after the `mouseout` callback got called. The issue is that `InteractionManager.update` checks for hits with the last recorded mouse coords even when the mouse has left the canvas.

I've updated "example 6 - Interactivity" to demonstrate the issue. The top-right button is clipped by the edge of the canvas. Hover over the button, then move the mouse off the canvas without leaving the the button. The button will flash its default state before returning to its hover state. I've verified that this PR fixes the issue.

Add `?w=1` to the url to ignore whitespace changes in the diff. My editor stripped all trailing whitespace.