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**
false,
            'checked',
          );
          expect(changeCount).toBe(0);
        });
        
        
        xit(
          'should not blow away user-entered text on successful reconnect to an uncontrolled textarea',
          () =>
            testUserInteractionBeforeClientRender(
              <textarea defaultValue="Hello" />,
            ),
        );
        
        
        xit(
          'should not blow away user-entered text on successful reconnect to a controlled textarea',
          async () => {
            let changeCount = 0;
            await testUserInteractionBeforeClientRender(
              <ControlledTextArea onChange={() => changeCount++} />,
            );
            expect(changeCount).toBe(0);
          },
        );
        it('should not blow away user-selected value on successful reconnect to an uncontrolled select', () =>
          testUserInteractionBeforeClientRender(
            <select defaultValue="Hello">
              <option key="1" value="Hello">Hello</option>