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**
}
      props = Object.assign({}, props, {
        value: undefined,
        children: '' + initialValue,
      });
    } else if (tag === 'select') {
      if (__DEV__) {
        ReactControlledValuePropTypes.checkPropTypes(
          'select',
          props,
          () => '', 
        );
        for (var i = 0; i < valuePropNames.length; i++) {
          var propName = valuePropNames[i];
          if (props[propName] == null) {
            continue;
          }
          var isArray = Array.isArray(props[propName]);
          if (props.multiple && !isArray) {
            warning(
              false,
              'The `%s` prop supplied to <select> must be an array if ' +
                '`multiple` is true.%s',
              propName,
              '', 
            );
          } else if (!props.multiple && isArray) {
            warning(
              false,
              'The `%s` prop supplied to <select> must be a scalar ' +