Stop polyfilling intersection-observer; Safari's supported this since v12.1

package.json

@@ -43,7 +43,6 @@
     "dompurify": "^2.0.11",
     "i18next": "^19.5.0",
     "icomcom-react": "^1.0.1",
-    "intersection-observer": "^0.10.0",
     "isomorphic-unfetch": "^3.0.0",
     "jss": "^10.3.0",
     "jss-rtl": "^0.3.0",

src/components/GalleryViewThumbnail.js

@@ -5,7 +5,6 @@ import Chip from '@material-ui/core/Chip';
 import AnnotationIcon from '@material-ui/icons/CommentSharp';
 import SearchIcon from '@material-ui/icons/SearchSharp';
 import classNames from 'classnames';
-import 'intersection-observer'; // polyfill needed for Safari
 import IntersectionObserver from '@researchgate/react-intersection-observer';
 import MiradorCanvas from '../lib/MiradorCanvas';
 import IIIFThumbnail from '../containers/IIIFThumbnail';

src/components/IIIFThumbnail.js

 import React, { Component } from 'react';
 import PropTypes from 'prop-types';
-import 'intersection-observer'; // polyfill needed for Safari
 import Typography from '@material-ui/core/Typography';
 import IntersectionObserver from '@researchgate/react-intersection-observer';
 import classNames from 'classnames';