How to remove left tip of the "Back" button at Navigation Bar?

[devyn]

Normally, it's great to have such 'back' button with a tip pointing to the left. However, I just want to use my custom background to that back button and the result is quite funny. How can get rip of that tip? Here is the screenshot. Thanks

[mitchellsimoens]

Give the back button a different ui..

navigationBar : {
    backButton : {
        align : 'left',
        hidden  : true,
        ui : 'something-here'
    }
}