message: add forwardRef to BarButton
diff: import React from 'react';
  import { requireNativeComponent, Image, Platform, UIManager, View, StyleSheet } from 'react-native';
  -const BarButton = ({image, show, search, style, children, ...props}) => {
  +const BarButton = React.forwardRef<typeof NVBarButton, any>(({image, show, search, style, children, ...props}, ref) => {
  var constants = (UIManager as any).getViewManagerConfig('NVNavigationBar').Constants;
  return (Platform.OS === 'android' || !search) && (
  <NVBarButton
  + ref={ref}
  search={search}
  showActionView={!!children}
  showAsAction={Platform.OS === 'android' ? constants.ShowAsAction[show] : null}
  @@ -13,7 +14,7 @@ const BarButton = ({image, show, search, style, children, ...props}) => {
  children={children}
  {...props} />
  )
  -}
  +})
  const NVBarButton = requireNativeComponent<any>('NVBarButton', null)
  