Fix tests

Author: stephane-monnot

__tests__/VerticalTimelineElement_test.js

@@ -1,3 +1,6 @@
+/**
+ * @jest-environment jsdom
+ */
 import React from 'react';
 import {
   renderIntoDocument,

__tests__/VerticalTimeline_test.js

@@ -1,3 +1,6 @@
+/**
+ * @jest-environment jsdom
+ */
 import React from 'react';
 import { shallow } from 'enzyme';
 import { expect } from 'chai';