headerTintColor not working when using Actions.push

### Version
Tell us which versions you are using:

- react-native-router-flux v4.0.6
- react v16.8.3
- react-native v0.59.1

### Expected behaviour
Left back icon colour should be white

### Actual behaviour
headerTintColor="white" is ignored

### Steps to reproduce
When i use
```javascript
Actions.push('Scene_2')
```
instead of
```javascript
Actions.Scene_2()
```
Is there a difference between push and Actions\[key\]()?

### Reproducible Demo
```javascript
import React, { Component } from 'react';
import { StyleSheet, Text, View } from 'react-native';
import { Scene, Router, Actions, Stack, Lightbox, Modal } from 'react-native-router-flux';

import Button from 'react-native-button';

const styles = StyleSheet.create({
container: {
flex: 1,
justifyContent: 'center',
alignItems: 'center',
backgroundColor: '#F5FCFF',
},
scene: {
backgroundColor: '#F5FCFF',
shadowOpacity: 1,
shadowRadius: 3,
},
});

export class Main extends Component {
render() {
return (

Main
Actions.PostLogin({type:'replace'})}>Login
Actions.Scene_1()}>Go To Scene_1
Actions.push('Scene_2')}>Go To Scene_2

);
}
}
export class Scene_1 extends Component {
render() {
return (

Scene_1
Back

);
}
}
export class Scene_2 extends Component {
render() {
return (

Scene_2
Back

);
}
}
export default class RouterComponent extends Component {
render() {
return (

);
}
}
```