message: fix yarn build problem
diff: -import * as React from 'react';
  +import React, {Component } from 'react';
  import s from './App.css'
  -export default class App extends React.Component {
  +export default class App extends Component {
  render() {
  return (
  <div className={s.appGrid}>
  <div className={s.empty} />
  <div className={s.topmenu}><h2>PETSCII EDITOR</h2></div>
  - <div className={s.leftmenubar}>
  - </div>
  + <div className={s.leftmenubar} />
  <div className={s.editor}>
  {this.props.children}
  </div>
  