message: docs(SwipeCell): use composition api
diff: @@ -71,9 +71,11 @@ app.use(SwipeCell);
  ```
  ```js
  +import { Dialog } from 'vant';
  +
  export default {
  - methods: {
  - beforeClose({ position, instance }) {
  + setup() {
  + const beforeClose = ({ position }) => {
  switch (position) {
  case 'left':
  case 'cell':
  @@ -81,14 +83,14 @@ export default {
  return true;
  case 'right':
  return new Promise((resolve) => {
  - this.$dialog
  - .confirm({
  - message: 'Are you sure to delete?',
  - })
  - .then(resolve);
  + Dialog.confirm({
  + title: 'Are you sure to delete?',
  + }).then(resolve);
  });
  }
  - },
  + };
  +
  + return { beforeClose };
  },
  };
  ```
  