What happened

Updated a Repo to React 16 and discovered that iterating over a Map will render the return item && the key. I realize using Maps as children is experimental but thought you'd like to know. Not sure if this would be considered a react 16 bug.

What I expected:
Render the React element and ignore the key.

How to reproduce

type ItemMap = Map<*, *>;
const itemMap: ItemMap = Map({
  0: 'zero',
  1: 'one',
  2: 'two',
});

{itemMap.map((item, index) => (
  <Item key={index} item={item} />
)}

will render something like 0 <Item /> 1 <Item /> 3 <Item />