title: Customizing default navigation bar of react-native-router-flux
body: <p>I am using <code>react native router flux</code> for navigation in my react native project. <code>Router flux</code> has a default <code>navBar</code>. </p>
  
  <p>Is there a way to customize the <code>navBar</code>? like, changing colour of text and background. </p>
  
  <p>I tried editing the file in <code>node_modules/react-native-router-flux/src/navBar.js</code> but it doesn't seem to work. </p>
  
  <p>Please help me.</p>