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".
return this.renderDOM(child, context, parentNamespace);
        } else {
          var children = toArray(child);
          var frame = {
            domNamespace: parentNamespace,
            children,
            childIndex: 0,
            context: context,
            footer: '',
          };
          if (__DEV__) {
            frame.debugElementStack = [];
          }
          this.stack.push(frame);
          return '';
        }
      }
    }
  }
  renderDOM(element, context, parentNamespace) {
    var tag = element.type.toLowerCase();
    let namespace = parentNamespace;
    if (parentNamespace === Namespaces.html) {
      namespace = getIntrinsicNamespace(tag);
    }
    if (__DEV__) {
      if (namespace === Namespaces.html) {
        
        
        warning(