message: payorder add tip slot
diff: <template>
  <div class="van-pay-order">
  - <div class="van-pay-order__tip" v-show="tip">{{ tip }}</div>
  + <div class="van-pay-order__tip" v-show="tip || hasTipSlot">{{ tip }}<slot name="tip" /></div>
  <div class="van-pay-order__bar">
  <div class="van-pay-order__price">
  <template v-if="hasPrice">
  @@ -49,6 +49,9 @@ export default {
  priceDecimal() {
  const decimal = this.price % 100;
  return (decimal < 10 ? '0' : '') + decimal;
  + },
  + hasTipSlot () {
  + return !!this.$slots['tip']
  }
  },
  