Observed this on react@16.0.0-beta.5

```js
import React from 'react';
import { renderToString } from 'react-dom/server';

const B = () => 'b';

console.log(renderToString(<div>{'a'}<B />{'c'}</div>));
```

This renders as `<div data-reactroot="">a<!-- -->bc</div>`. If you try to hydrate this you'll get the error: Text content did not match. Server: "bc" Client: "b".
jest.resetModuleRegistry();
  
  ExecutionEnvironment = require('ExecutionEnvironment');
  PropTypes = require('prop-types');
  React = require('react');
  ReactDOM = require('react-dom');
  ReactTestUtils = require('react-dom/test-utils');
  
  
  
  jest.resetModuleRegistry();
  ReactDOMServer = require('react-dom/server');
}
describe('ReactDOMServerIntegration', () => {
  beforeEach(() => {
    resetModules();
    ExecutionEnvironment.canUseDOM = false;
  });
  describe('basic rendering', function() {
    itRenders('a blank div', async render => {
      const e = await render(<div />);
      expect(e.tagName).toBe('DIV');
    });
    itRenders('a self-closing tag', async render => {
      const e = await render(<br />);
      expect(e.tagName).toBe('BR');
    });
    itRenders('a self-closing tag as a child', async render => {