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**
<option key="2" value="Goodbye">Goodbye</option>
            </select>,
          ));
        it('should not blow away user-selected value on successful reconnect to an controlled select', async () => {
          let changeCount = 0;
          await testUserInteractionBeforeClientRender(
            <ControlledSelect onChange={() => changeCount++} />,
          );
          expect(changeCount).toBe(0);
        });
      });
    });
  });
  describe('context', function() {
    let PurpleContext, RedContext;
    beforeEach(() => {
      class Parent extends React.Component {
        getChildContext() {
          return {text: this.props.text};
        }
        render() {
          return this.props.children;
        }
      }
      Parent.childContextTypes = {text: PropTypes.string};
      PurpleContext = props => <Parent text="purple">{props.children}</Parent>;
      RedContext = props => <Parent text="red">{props.children}</Parent>;
    });
    itRenders('class child with context', async render => {
      class ClassChildWithContext extends React.Component {