Nodes are not reused properly when adding/removing them

The issue is likely to be upstream (https://github.com/romseguy/d3-state-visualizer/issues/12), but I still decided to report it here as well until the dependency is upgraded. For those who're wondering if this is what they see too, here is a quick gif of the bug:

![anim](https://cloud.githubusercontent.com/assets/608862/21022165/7ed478ca-bd73-11e6-9e3c-48ad2a4a4f18.gif)
