message: docs(SwipeCell): change "slot" to "v-slot"
diff: @@ -15,11 +15,11 @@ Vue.use(SwipeCell);
  ```html
  <van-swipe-cell>
  - <template slot="left">
  + <template #left>
  <van-button square type="primary" text="Select" />
  </template>
  <van-cell :border="false" title="Cell" value="Cell Content" />
  - <template slot="right">
  + <template #right>
  <van-button square type="danger" text="Delete" />
  <van-button square type="primary" text="Collect"/>
  </template>
  @@ -38,13 +38,14 @@ Vue.use(SwipeCell);
  class="goods-card"
  thumb="https://img.yzcdn.cn/vant/cat.jpeg"
  />
  + <template #right>
  <van-button
  - slot="right"
  square
  text="Delete"
  type="danger"
  class="delete-button"
  />
  + </template>
  </van-swipe-cell>
  <style>
  @@ -63,11 +64,11 @@ Vue.use(SwipeCell);
  ```html
  <van-swipe-cell :before-close="beforeClose">
  - <template slot="left">
  + <template #left>
  <van-button square type="primary" text="Select" />
  </template>
  <van-cell :border="false" title="Cell" value="Cell Content" />
  - <template slot="right">
  + <template #right>
  <van-button square type="danger" text="Delete" />
  </template>
  </van-swipe-cell>
  