change type of THREE.Quaternion.setFromUnitVectors

I think the parameter type should be Vector3.

[ref](https://github.com/mrdoob/three.js/blob/master/src/math/Quaternion.js#L257)  
[ref](http://threejs.org/docs/#Reference/Math/Quaternion)
Merge pull request #3284 from yutopp/patch-1

change type of THREE.Quaternion.setFromUnitVectors