title: goBack always taking to home/first screen in react-navigation
body: <p>I am working on an app but goback button is not taking me to the back screen.</p>
  
  <p>App.js</p>
  
  <pre><code>import React, { Component } from 'react';
  import one from './components/test/one';
  import two from './components/test/two';
  import three from './components/test/three';
  
  import { DrawerNavigator } from 'react-navigation';
  
  const AppNavigator = DrawerNavigator({
      one: {
        screen: one,
      },
      two: {
        screen: two,
      },
      three: {
        screen: three,
      },
    }
  );
  
  export default () =&gt;
        &lt;AppNavigator /&gt;;
  </code></pre>
  
  <p>components/test/one.js</p>
  
  <pre><code>import React, { Component } from 'react';
  import { Button } from 'react-native';
  
  export default class one extends React.Component {
    static navigationOptions = {
      drawerLabel: 'one',
    };
  
    render() {
      return (
        &lt;Button
          onPress={() =&gt; this.props.navigation.navigate('two')}
          title="Go to Two"
        /&gt;
      );
    }
  }
  </code></pre>
  
  <p>components/test/two.js</p>
  
  <pre><code>import React, { Component } from 'react';
  import { Button } from 'react-native';
  
  export default class two extends React.Component {
    static navigationOptions = {
      drawerLabel: 'two',
    };
  
    render() {
      return (
        &lt;Button
          onPress={() =&gt; this.props.navigation.navigate('three')}
          title="Go to 3"
        /&gt;
      );
    }
  }
  </code></pre>
  
  <p>components/test/three.js</p>
  
  <pre><code>import React, { Component } from 'react';
  import { Button } from 'react-native';
  
  export default class three extends React.Component {
    static navigationOptions = {
      drawerLabel: 'three',
    };
  
    render() {
      return (
        &lt;Button
          onPress={() =&gt; this.props.navigation.goBack()}
          title="Go back to 2"
        /&gt;
      );
    }
  }
  </code></pre>
  
  <p>click on "Go to two" => "Go to 3" => "Go back to 2".
  on screen 3, clicking on the "Go back to 2" is always taking me to one.js.</p>
  
  <p>It is not even working if I combine them in one single file.</p>