Back button Warning

[ajoshdee]

Version

v3 is SLOW for Android right now (because React Native ExperimentalNavigation is slow), see #355, no need to create new issue!
Tell us which versions you are using (react native 0.22 is required for v3!):

• react-native-router-flux v3.2.8
• react-native v0.22.0

Expected behaviour

No warning when onLeft is not specified

Actual behaviour

Warning shows up when onLeft is not specified

Steps to reproduce

1. Add a scene (without specifying onLeft closure but with leftTitle)
2. Push to the scene

[ajoshdee]

I just want the normal back button.

[aksonov]

You have to use backTitle then i guess.