message: Gave tabs correct index
  Filtered out null children otherwise removing tab 1 (by setting to null) from tabs 0, 1, 2  ends up with last tab still with index 2
diff: @@ -33,9 +33,11 @@ class TabBar extends React.Component<any, any> {
  selectedTab={this.state.selectedTab}
  style={styles.tabBar}>
  <BackButton onPress={this.handleBack} />
  - {React.Children.map(children, (child: any, index) => {
  + {React.Children.toArray(children)
  + .filter(child => !!child)
  + .map((child: any, index) => {
  var selected = index === this.state.selectedTab;
  - return child && React.cloneElement(child, {...child.props, selected});
  + return child && React.cloneElement(child, {...child.props, selected})
  })}
  </NVTabBar>
  </>
  