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**
return (
              <select
                value={this.state.value}
                onChange={this.handleChange.bind(this)}>
                <option key="1" value="Hello">Hello</option>
                <option key="2" value="Goodbye">Goodbye</option>
              </select>
            );
          }
        };
      });
      describe('user interaction with controlled inputs', function() {
        itClientRenders('a controlled text input', async render => {
          let changeCount = 0;
          const e = await render(
            <ControlledInput onChange={() => changeCount++} />,
          );
          expect(changeCount).toBe(0);
          expect(e.value).toBe('Hello');
          
          e.value = 'Goodbye';
          ReactTestUtils.Simulate.change(e);
          expect(changeCount).toBe(1);
          expect(e.value).toBe('Goodbye');
        });
        itClientRenders('a controlled textarea', async render => {
          let changeCount = 0;