Transition: Transition.Group doesn't perform transitions correctly

[inspiral]

Steps to Reproduce

1. Adding at least 2 new elements with the '+' sign, then trying to remove elements with the '-' results errorneous behaviour, since the list items will not disappear properly according to the clicks on '-'.

Expected
The Transition should do remove item 1 by 1 when i click on the '-' sign.

Result
The Transition does not do this

Testcase
If the docs show the issue, use: https://react.semantic-ui.com/modules/transition#transition-example-group
Otherwise, fork this to get started: http://codepen.io/levithomason/pen/ZpBaJX

[layershifter]

@ianunruh Thanks for your eyes, it's caused by #2047. PR is coming.