import React, { Component } from 'react';

export default class App extends Component {
  render() {
    return (
      <h1>Hello React :)</h1>
    );
  };

}

import React, { Component } from 'react';

export default class App extends Component {
  render() {
    return (
      <h1>Hello React :)</h1>
    );
  }
}

Remove extra semicolon