Crossfade collapsing titlebar background color (#1272)

android/app/src/main/java/com/reactnativenavigation/views/TitleBarBackground.java

@@ -12,6 +12,7 @@ public class TitleBarBackground extends TransitionDrawable {
 
     public TitleBarBackground(Drawable... drawables) {
         super(drawables);
+        setCrossFadeEnabled(true);
     }
 
     public void showTranslucentBackground() {