message: hide indicators when one swipe page
diff: <div class="van-swipe__items">
  <slot></slot>
  </div>
  - <div class="van-swipe__indicators" v-if="showIndicators">
  + <div
  + class="van-swipe__indicators"
  + v-if="showIndicators && swipes.length > 1"
  + >
  <span class="van-swipe__indicator" v-for="(item, index) in swipes.length" :key="index" :class="{
  'van-swipe__indicator--active': currIndex === index
  }">
  