**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`
const e = await render(<div><br /></div>);
      expect(e.childNodes.length).toBe(1);
      expect(e.firstChild.tagName).toBe('BR');
    });
    itRenders('a string', async render => {
      let e = await render('Hello');
      expect(e.nodeType).toBe(3);
      expect(e.nodeValue).toMatch('Hello');
    });
    itRenders('a number', async render => {
      let e = await render(42);
      expect(e.nodeType).toBe(3);
      expect(e.nodeValue).toMatch('42');
    });
    itRenders('an array with one child', async render => {
      let e = await render([<div key={1}>text1</div>]);
      let parent = e.parentNode;
      expect(parent.childNodes[0].tagName).toBe('DIV');
    });
    itRenders('an array with several children', async render => {
      let Header = props => {
        return <p>header</p>;
      };
      let Footer = props => {
        return [<h2 key={1}>footer</h2>, <h3 key={2}>about</h3>];
      };
      let e = await render([
        <div key={1}>text1</div>,
        <span key={2}>text2</span>,
        <Header key={3} />,