feat: upgrade to Emotion 10 (#2166)

packages/netlify-cms-ui-default/src/Toggle.js

@@ -1,6 +1,7 @@
 import React from 'react';
 import PropTypes from 'prop-types';
-import styled, { css } from 'react-emotion';
+import styled from '@emotion/styled';
+import { css } from '@emotion/core';
 import ReactToggled from 'react-toggled';
 import { colors, colorsRaw, shadows, transitions } from './styles';