message: Added defaultTab prop for uncontrolled scenario
  Works like defaultValue of React input
diff: @@ -6,11 +6,12 @@ class TabBar extends React.Component<any, any> {
  private ref: React.RefObject<View>;
  constructor(props) {
  super(props);
  - this.state = {selectedTab: props.tab || 0};
  + this.state = {selectedTab: props.tab || props.defaultTab};
  this.ref = React.createRef<View>();
  this.onTabSelected = this.onTabSelected.bind(this);
  }
  static defaultProps = {
  + defaultTab: 0,
  scrollable: false,
  primary: Platform.OS === 'ios',
  }
  