Use ES2017 output for Pixi3D 2.0?

[jnsmalm]

Since PixiJS will output ES2017 code starting from version 7, Pixi3D should probably do the same starting from version 2. Those users that still needs to support ES5, have to do the transpile. It will make the code smaller and faster for approx 95% of the users.

Thoughts?

[goldenratio]

I think it's a good change.