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**
constructor(props) {
            super(props);
            lifecycle.push('getInitialState');
            this.state = {name: 'TestComponent'};
          }
          componentWillMount() {
            lifecycle.push('componentWillMount');
          }
          componentDidMount() {
            lifecycle.push('componentDidMount');
          }
          render() {
            lifecycle.push('render');
            return <span>Component name: {this.state.name}</span>;
          }
          componentWillUpdate() {
            lifecycle.push('componentWillUpdate');
          }
          componentDidUpdate() {
            lifecycle.push('componentDidUpdate');
          }
          shouldComponentUpdate() {
            lifecycle.push('shouldComponentUpdate');
          }
          componentWillReceiveProps() {
            lifecycle.push('componentWillReceiveProps');
          }
          componentWillUnmount() {