Update vue-sortable.js

[wormen]

update described in #10

[jefflam]

@wormen This PR works for making Sortable work with Vue 2.0.. any idea why the checks are failing?

[sagalbot]

The checks fail because you can longer access the vm from the directive. That means that from the vm, you don't have a way to access the sortable instance, so all of the tests around assigning an ID fail.

I'm almost done a 2.0 compatible version which uses this inplementation for the directive, which can be used for simple situations, where you don't need to access the sortable instance from the vm. It will also include a sortable component that you may use when you need a more flexible implementation.

[haugen86]

Any closer to releasing the 2.0 compatible version, Sir? :-)

[alan-andrade]

I understand @sagalbot is working on v2.0 compatible. Does that mean this pr would get resolved as part of that work ? If not, what can we do to move this PR forward ?

Thanks.