message: docs(segment): set unique value for segment demo
diff: <!-- Icon end -->
  <ion-segment color="danger" scrollable value="map">
  - <ion-segment-button value="map" layout="icon-end">
  + <ion-segment-button value="call" layout="icon-end">
  <ion-icon name="call"></ion-icon>
  <ion-label>Call</ion-label>
  </ion-segment-button>
  