React Beautiful DnD example doesn't behave as expected

### Are you submitting a **bug report** or a **feature request**?
Bug

### What is the current behavior?

1) Add 3 items to the array in this sandbox: https://codesandbox.io/s/8k0ykyr7z9
2) Swap the 1st and 3rd item, and the list ends up reading 3-2-1 (because of the use of `.swap()` rather than `.move()`)

### What is the expected behavior?
The list should read 3-1-2.

### Sandbox Link
https://codesandbox.io/s/8k0ykyr7z9