Update test-compositing-order.html to use new Player syntax
Fix test-compositing-order.html

This intent of the test was broken by 1e21b9ee86fb7225494257a787dc9e0fbb5a01a5
though the test continued to pass.
Change compositing order to match new spec

For compositing, we now sort animations first by Player start time, and second
by DFS order within the Player's tree.

This fixes https://github.com/web-animations/web-animations-js/issues/100
Merge pull request #122 from steveblock/compositing

Change compositing order to match new spec