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 testMarkupMatch(serverElement, clientElement, true);
}
function expectMarkupMismatch(serverElement, clientElement) {
  return testMarkupMatch(serverElement, clientElement, false);
}
let onAfterResetModules = null;
function resetModules() {
  
  jest.resetModuleRegistry();
  if (typeof onAfterResetModules === 'function') {
    onAfterResetModules();
  }
  
  ExecutionEnvironment = require('ExecutionEnvironment');
  PropTypes = require('prop-types');
  React = require('react');
  ReactDOM = require('react-dom');
  ReactDOMFeatureFlags = require('ReactDOMFeatureFlags');
  ReactTestUtils = require('react-dom/test-utils');
  
  
  
  jest.resetModuleRegistry();
  if (typeof onAfterResetModules === 'function') {