bug: TransitionGroup assumes that at least two children will be present

[K4rakara]

On this line, the TransitionGroup component accesses the memo of its children. In the event that props.children is this:

[
  <div></div>,
]

then the memo of its children will resolve to just <div></div> instead of [<div></div>], which causes a type error on the next line, as a div itself is not spreadable.