message: docs(CouponList): use composition api
diff: @@ -18,20 +18,20 @@ app.use(CouponList);
  ```html
  <!-- Coupon Cell -->
  <van-coupon-cell
  - :coupons="coupons"
  - :chosen-coupon="chosenCoupon"
  - @click="showList = true"
  + :coupons="state.coupons"
  + :chosen-coupon="state.chosenCoupon"
  + @click="state.showList = true"
  />
  <!-- Coupon List -->
  <van-popup
  - v-model="showList"
  + v-model="state.showList"
  round
  position="bottom"
  style="height: 90%; padding-top: 4px;"
  >
  <van-coupon-list
  - :coupons="coupons"
  - :chosen-coupon="chosenCoupon"
  + :coupons="state.coupons"
  + :chosen-coupon="state.chosenCoupon"
  :disabled-coupons="disabledCoupons"
  @change="onChange"
  @exchange="onExchange"
  @@ -40,6 +40,8 @@ app.use(CouponList);
  ```
  ```js
  +import { reactive } from 'vue';
  +
  const coupon = {
  available: 1,
  originCondition: 0,
  @@ -53,22 +55,28 @@ const coupon = {
  };
  export default {
  - data() {
  - return {
  - chosenCoupon: -1,
  + setup() {
  + const state = reactive({
  coupons: [coupon],
  + showList: false,
  + chosenCoupon: -1,
  + });
  +
  + const onChange = (index) => {
  + state.showList = false;
  + state.chosenCoupon = index;
  + };
  + const onExchange = (code) => {
  + state.coupons.push(coupon);
  + };
  +
  + return {
  + state,
  + onChange,
  + onExchange,
  disabledCoupons: [coupon],
  };
  },
  - methods: {
  - onChange(index) {
  - this.showList = false;
  - this.chosenCoupon = index;
  - },
  - onExchange(code) {
  - this.coupons.push(coupon);
  - },
  - },
  };
  ```
  