修改返回箭头，自定义图标

class BackImage extends React.Component { //创建一个返回按钮的组件
  render() {
    return (
      <Image
        source={require('../../images/huo.png')}
        style={{ width: 8, height: 15}}
      />
    );
  }
}


navigationOptions: props => {
  return {
    headerTitle: '资讯详情',
    headerBackImage: <BackImage/>,
  }
}