**Do you want to request a *feature* or report a *bug*?**
Bug

**What is the current behavior?**
I've started recieving this warning about my SVGs which is using [feGaussianBlur](https://developer.mozilla.org/en-US/docs/Web/SVG/Element/feGaussianBlur): 
`Warning: Expected server HTML to contain a matching <feGaussianBlur> in <filter>.`

**What is the expected behavior?**
Should be no warnings because there are no difference.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
Such behavior started right after updating to `React 16.0.0-rc.3` and never happened with `React 15.6.1`
constructor(options) {
    super(options);
    this.buffer = '';
  }
  _write(chunk, encoding, cb) {
    this.buffer += chunk;
    cb();
  }
}
async function renderIntoStream(reactElement, errorCount = 0) {
  return await expectErrors(
    () =>
      new Promise(resolve => {
        let writable = new DrainWritable();
        ReactDOMServer.renderToNodeStream(reactElement).pipe(writable);
        writable.on('finish', () => resolve(writable.buffer));
      }),
    errorCount,
  );
}
async function streamRender(reactElement, errorCount = 0) {
  const markup = await renderIntoStream(reactElement, errorCount);
  var domElement = document.createElement('div');
  domElement.innerHTML = markup;
  return domElement.firstChild;
}
const clientCleanRender = (element, errorCount = 0) => {
  const div = document.createElement('div');