title: I want to show Icon on rightButtonImage by react-native-vector icon and react-native-router-flux
body: <p>I want to show right button on navigation var, but nothing rendered.
  Please give me solution or some advice.</p>
  
  <p><a href="https://i.stack.imgur.com/WNrcM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WNrcM.png" alt="enter image description here"></a></p>
  
  <p>Error</p>
  
  <blockquote>
    <p>ExceptionsManager.js:73 Warning: Cannot update during an existing state transition (such as within <code>render</code> or another component's constructor). Render methods should be a pure function of props and state; constructor side-effects are an anti-pattern, but can be moved to <code>componentWillMount</code>.</p>
  </blockquote>
  
  <p>Environment</p>
  
  <pre><code>    "react": "16.0.0-alpha.12",
      "react-native": "0.47.1",
      "react-native-router-flux": "^4.0.0-beta.17",
      "react-native-vector-icons": "^4.3.0"
  </code></pre>
  
  <p>App.js </p>
  
  <pre><code>import React, { Component } from 'react';
  import Router from './Router';
  
  class App extends Component {
      render() {
          return (
              &lt;Router /&gt;
          )
      }
  }
  export default App;
  </code></pre>
  
  <p>Router.js</p>
  
  <pre><code>import React, { Component } from 'react';
  import { View } from 'react-native'
  import { Actions, Scene, Router } from 'react-native-router-flux';
  import Icon from 'react-native-vector-icons/Ionicons';
  
  import Home from './components/Home';
  import Menu from './components/Menu';
  
  class RouterComponent extends Component {
  
      constructor(){
          super()
          this.state = {bookIcon: null}
      }
  
      componentWillMount(){
          Icon.getImageSource('ios-book', 30).then(source =&gt; 
          this.setState({bookIcon:source}));
      }
  
      render(){
          return (
              &lt;Router&gt;
                  &lt;Scene key="container"&gt;
                      &lt;Scene
                          key="home" component={Home}
                          initial={true}
                          title={"Home"}
                          rightButtonImage={this.state.bookIcon}
                          rightButtonIconStyle={{ width: 30, height: 30 }}
                          onRight={ () =&gt; Actions.Menu() }
                      /&gt;
                      &lt;Scene
                          key="menu"
                          component={Menu}
                          title={"Menu"}
                      /&gt;
                  &lt;/Scene&gt;
              &lt;/Router&gt;
          )
      }
  };
  export default RouterComponent;
  </code></pre>
  
  <ul>
  <li>Home.js and Menu.js just show Text component</li>
  </ul>
  
  <p>Thank you for reading my problem.</p>