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".
getChildContext() {
            return {text: this.state.text};
          }
          componentWillMount() {
            this.setState({text: 'foo'});
          }
          render() {
            return <Child />;
          }
        }
        WillMountContext.childContextTypes = {text: PropTypes.string};
        const Child = (props, context) => {
          return <div>{context.text}</div>;
        };
        Child.contextTypes = {text: PropTypes.string};
        const e = await render(<WillMountContext />);
        expect(e.textContent).toBe('foo');
      },
    );
    itThrowsWhenRendering(
      'if getChildContext exists without childContextTypes',
      render => {
        class MyComponent extends React.Component {
          render() {
            return <div />;
          }
          getChildContext() {