**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`
<Footer key={4} />,
      ]);
      let parent = e.parentNode;
      expect(parent.childNodes[0].tagName).toBe('DIV');
      expect(parent.childNodes[1].tagName).toBe('SPAN');
      expect(parent.childNodes[2].tagName).toBe('P');
      expect(parent.childNodes[3].tagName).toBe('H2');
      expect(parent.childNodes[4].tagName).toBe('H3');
    });
    itRenders('a nested array', async render => {
      let e = await render([
        [<div key={1}>text1</div>],
        <span key={1}>text2</span>,
        [[[null, <p key={1} />], false]],
      ]);
      let parent = e.parentNode;
      expect(parent.childNodes[0].tagName).toBe('DIV');
      expect(parent.childNodes[1].tagName).toBe('SPAN');
      expect(parent.childNodes[2].tagName).toBe('P');
    });
    itRenders('an iterable', async render => {
      const threeDivIterable = {
        '@@iterator': function() {
          var i = 0;
          return {
            next: function() {
              if (i++ < 3) {
                return {value: <div key={i} />, done: false};
              } else {
                return {value: undefined, done: true};