fix(Segment): using loading and clearing together makes clearing lose its effect

[rkosafo]

Steps to Reproduce

1. Using the loading sample, replace image with right floated button
2. Add clearing to the segment

Expected
The Segment should be large enough to contain the button.

Result
The Segment shrinks in size as if clearing has not been applied.

Testcase
If the docs show the issue, use: http://react.semantic-ui.com/elements/segment
Otherwise, fork this to get started: http://codepen.io/levithomason/pen/ZpBaJX

import React from 'react'
import { Image, Segment, Button } from 'semantic-ui-react'

const SegmentExampleLoading = () => (
  <Segment clearing loading>
    <Button floated="right">Test</Button>
  </Segment>
)

export default SegmentExampleLoading

[levithomason]

As with #1384, this also seems sane to me, however, this is also a CSS issue and therefore should be posted on https://github.com/Semantic-Org/Semantic-UI.