Update Youtube VideoPreview component tests for horizontal mode

VideoPreview.unit.test.js

import React from 'react';
import {shallow} from 'enzyme';
import {VideoPreview} from '../VideoPreview';

describe('VideoPreview', () => {
  test('renders vertically', () => {
    const wrapper = shallow(<VideoPreview/>);
    expect(wrapper).toMatchSnapshot();
  });
  test('renders horizontally', () => {
    const wrapper = shallow(<VideoPreview horizontal={true}/>);
    expect(wrapper).toMatchSnapshot();
  });
});