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**
}
      runTest();
      
      ExecutionEnvironment.canUseDOM = true;
      runTest();
    });
    it('should have the correct mounting behavior', () => {
      
      ExecutionEnvironment.canUseDOM = true;
      var mountCount = 0;
      var numClicks = 0;
      class TestComponent extends React.Component {
        componentDidMount() {
          mountCount++;
        }
        click = () => {
          numClicks++;
        };
        render() {
          return (
            <span ref="span" onClick={this.click}>Name: {this.props.name}</span>
          );
        }
      }
      var element = document.createElement('div');
      ReactDOM.render(<TestComponent />, element);
      var lastMarkup = element.innerHTML;
      
      
      ReactDOM.render(<TestComponent name="x" />, element);