title: Icon not displaying on screen android using react-native-vector-icons
body: <p>I am using <a href="https://github.com/react-community/create-react-native-app" rel="nofollow noreferrer">create-react-native-app</a>. I want to use <a href="https://github.com/oblador/react-native-vector-icons" rel="nofollow noreferrer">react-native-vector-icons</a></p>
  
  <p>But its not showing anything on android screen (I am viewing it on expo app)</p>
  
  <p>Here is what I did:</p>
  
  <p>App.js:</p>
  
  <pre><code>       const Courses = TabNavigator({
    ReactCourses: { screen: ReactCourses },
    NativeCourses: { screen: NativeCourses },
  }, {
    tabBarOptions: {
      activeTintColor: '#e91e63',
      swipeEnabled: true,
      showIcon:true,
    },
  });
  </code></pre>
  
  <p>ReactCourses.js:</p>
  
  <pre><code>     import Icon from 'react-native-vector-icons/MaterialIcons';
      static navigationOptions = {
      tabBarLabel: 'React Courses',
      tabBarIcon:({ tintColor }) =&gt; (
          &lt;Icon
            name={'home'}
            size={26}
            style={[styles.icon, {color: tintColor}]} /&gt;
        )
  
    }
  </code></pre>