Invalid tenary expressions in example code snippets in README

[calebpitan]

Tenary expressions in code snippets written in the README.md file are invalid.

class ChildComponent extends Component {
 // ...

  render () {
    return (
      <div>
        <button onClick={this.handleClick} />
        { this.state.show ? <div /> } // invalid expression here
      </div>
    )
  }
}