**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`
expectTextNode(e.childNodes[0], 'Text');
        expect(spanNode.tagName).toBe('SPAN');
        expect(spanNode.childNodes.length).toBe(1);
        expectNode(spanNode.firstChild, TEXT_NODE_TYPE, 'More Text');
      });
      itRenders('a non-standard element with text', async render => {
        const e = await render(<nonstandard>Text</nonstandard>);
        expect(e.tagName).toBe('NONSTANDARD');
        expect(e.childNodes.length).toBe(1);
        expectNode(e.firstChild, TEXT_NODE_TYPE, 'Text');
      });
      itRenders('a custom element with text', async render => {
        const e = await render(<custom-element>Text</custom-element>);
        expect(e.tagName).toBe('CUSTOM-ELEMENT');
        expect(e.childNodes.length).toBe(1);
        expectNode(e.firstChild, TEXT_NODE_TYPE, 'Text');
      });
      itRenders('a leading blank child with a text sibling', async render => {
        const e = await render(<div>{''}foo</div>);
        if (render === serverRender || render === streamRender) {
          expect(e.childNodes.length).toBe(1);
          expectTextNode(e.childNodes[0], 'foo');
        } else {
          expect(e.childNodes.length).toBe(2);
          expectTextNode(e.childNodes[0], '');
          expectTextNode(e.childNodes[1], 'foo');
        }
      });
      itRenders('a trailing blank child with a text sibling', async render => {
        const e = await render(<div>foo{''}</div>);