DragDropMonitor failes to notify subscribeToStateChange subscribers in some cases

[mattiasgronlund]

Currently dnd-core takes for granted that it store.subscribe() will notify all state changes. But redux does not guarantee that, e.g. when an earlier subscription dispatches a new action to the store.

The consequence is that render() will not always be called when needed.

[dan]

Out in 1.3.0, thanks!