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 describeComponentFrame(name, source, ownerName);
  };
  var {ReactDebugCurrentFrame} = require('ReactGlobalSharedState');
  var currentDebugStack = null;
  var currentDebugElementStack = null;
  var setCurrentDebugStack = function(stack) {
    currentDebugElementStack = stack[stack.length - 1].debugElementStack;
    
    currentDebugElementStack.length = 0;
    currentDebugStack = stack;
    ReactDebugCurrentFrame.getCurrentStack = getStackAddendum;
  };
  var pushElementToDebugStack = function(element) {
    if (currentDebugElementStack !== null) {
      currentDebugElementStack.push(element);
    }
  };
  var resetCurrentDebugStack = function() {
    currentDebugElementStack = null;
    currentDebugStack = null;
    ReactDebugCurrentFrame.getCurrentStack = null;
  };
  var getStackAddendum = function(): null | string {
    if (currentDebugStack === null) {
      return null;
    }
    let stack = '';
    let debugStack = currentDebugStack;
    for (let i = debugStack.length - 1; i >= 0; i--) {
      let debugElementStack = debugStack[i].debugElementStack;