order changed

Main.js

render() {
    const nav = <header key="nav">{this.renderNav()}</header>;
    const content = <main key="content">{this.renderContent()}</main>;

    const { showOnTop } = this.props;
    return (
      <React.Fragment>
        {showOnTop ? [nav, content] : [content, nav]}
      </React.Fragment>
    );
  }