React 16 alpha allows returning array in render function but server renderer expects children to always be react elements

```
TypeError: Cannot read property 'toLowerCase' of undefined
    at ReactDOMServerRenderer.renderDOM
```

source
```javascript
function renderDOM(element, context) {
    var tag = element.type.toLowerCase(); // element is array
```

Fiddle: https://jsfiddle.net/84v837e9/160/

**react@16.0.0-alpha.13**
queue = null;
        replace = false;
        if (oldReplace && oldQueue.length === 1) {
          inst.state = oldQueue[0];
        } else {
          var nextState = oldReplace ? oldQueue[0] : inst.state;
          var dontMutate = true;
          for (var i = oldReplace ? 1 : 0; i < oldQueue.length; i++) {
            var partial = oldQueue[i];
            var partialState = typeof partial === 'function'
              ? partial.call(inst, nextState, child.props, publicContext)
              : partial;
            if (partialState) {
              if (dontMutate) {
                dontMutate = false;
                nextState = Object.assign({}, nextState, partialState);
              } else {
                Object.assign(nextState, partialState);
              }
            }
          }
          inst.state = nextState;
        }
      } else {
        queue = null;
      }
    }
    child = inst.render();
    if (__DEV__) {
      if (child === undefined && inst.render._isMockFunction) {