message: [Doc] ImagePreview: fix typo
diff: @@ -58,7 +58,7 @@ setTimeout(() => {
  :images="images"
  @change="onChange"
  >
  - <template v-slot:index>Page: { index }</template>
  + <template v-slot:index>Page: {{ index }}</template>
  </van-image-preview>
  ```
  