the behavior of transiton event in v3 is diffrent of v2.

[underfin]

What problem does this feature solve?

In v2, Theonleave event be triggered before nextFrame event.
But in v3,Theonleave event be triggered after nextFrame.
As same as enter and beforeEnter.
And I don't find this change in rfc.

// v3 test
waitForUpdate(() => {
        expect(beforeLeaveSpy).toHaveBeenCalledWith(_el)
      }).thenWaitFor(nextFrame).then(() => {
        expect(onLeaveSpy).toHaveBeenCalledWith(_el)
      }).
// v2 test
waitForUpdate(() => {
        expect(beforeLeaveSpy).toHaveBeenCalledWith(_el)
        expect(onLeaveSpy).toHaveBeenCalledWith(_el)
      }).thenWaitFor(nextFrame).then(() => {
      })

What does the proposed API look like?

Maybe should keep the behavior with v2.

[underfin]

If it is need to fix.I will pull a pr.

[underfin]

I re-think this. Maybe this change is not break user upgarde v3.So can we just do this?