Actions.currentScene in Tabs with tabBarComponent will get wrong scene name

### Version
Tell us which versions you are using:
- react-native-router-flux 4.0.6
- react 16.8.6
- react-native 0.60.4

### Expected behaviour
Actions.currentScene should be get correct scene name.

### Actual behaviour
But it get `_SceneName` not `SceneName`

### Steps to reproduce
For non-obvious bugs, please fork this component, modify Example project to reproduce your issue and include link here.
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### Reproducible Demo
1. App.js
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2. Home.js & Profile.js
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Home

```
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Profile

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3. Footer.js
```

Actions.jump('Home')}>

Actions.jump('Profile')}>


```