**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 B = () => 'b';
          const e = await render(<div>{'a'}<B />{'c'}</div>);
          if (
            render === serverRender ||
            render === clientRenderOnServerString ||
            render === streamRender
          ) {
            
            expect(e.childNodes.length).toBe(5);
            expectTextNode(e.childNodes[0], 'a');
            expectTextNode(e.childNodes[2], 'b');
            expectTextNode(e.childNodes[4], 'c');
          } else {
            expect(e.childNodes.length).toBe(3);
            expectTextNode(e.childNodes[0], 'a');
            expectTextNode(e.childNodes[1], 'b');
            expectTextNode(e.childNodes[2], 'c');
          }
        },
      );
      itRenders('a tree with sibling host and text nodes', async render => {
        class X extends React.Component {
          render() {
            return [null, [<Y key="1" />], false];
          }
        }
        function Y() {
          return [<Z key="1" />, ['c']];
        }
        function Z() {