message: Rendered image only if provided
  Doesn't quite match android because would render a gap on primary tabs (I think), but don't expect some tabs with images and some without so simpler not to render
diff: @@ -51,7 +51,9 @@ class TabBar extends React.Component<any, any> {
  return (
  <TouchableHighlight key={i} href={href} onPress={(e) => this.changeTab(i, e)} style={{flex: 1}}>
  <View style={{alignItems: 'center', height, backgroundColor: barTintColor, paddingTop, borderBottomWidth: highlight ? 2 : 0, borderBottomColor: highlight ? color : undefined}}>
  + {image && (
  <Image source={image} accessibilityLabel={title} style={{width: 24, height: 24, tintColor: color}} />
  + )}
  {title && (
  <Text style={{textTransform: !primary ? 'uppercase' : undefined, fontFamily, fontWeight, fontStyle, fontSize, lineHeight: !primary ? 20 : 12, marginTop: !primary ? 4 : 0, color: color}}>{title}</Text>
  )}
  