from/to states passed in should not be mutated

[cheapsteak]

Problem:

import animate from 'gsap-promise';

const from = {opacity: 0};
const to = {opacity: 1};

Promise.all([
    animate.fromTo(el1, 0.5, from, to),
    animate.fromTo(el2, 0.5, from, to),
])

The first promise never resolves because the onComplete is overwritten by the second call

This would be solved if the object is shallow cloned before having options added on by the library

Current workaround

Defensively clone everything passed into gsap-promise

Promise.all([
    animate.fromTo(el1, 0.5, {...from}, {...to}),
    animate.fromTo(el2, 0.5, {...from}, {...to}),
])

[mattdesl]

:+1: We can use object-assign for this.

[cheapsteak]

pushed fix to master along with new test would adding a dependency justify bumping a minor version or should it just be a patch?

[mattdesl]

Just a patch since the API didn't change and there are no new features added