message: feat(cli): DemoBlock add card style
diff: <template>
  <div class="van-doc-demo-block">
  <h2 class="van-doc-demo-block__title">{{ title }}</h2>
  + <div v-if="card" class="van-doc-demo-block__card">
  <slot />
  </div>
  + <slot v-else />
  + </div>
  </template>
  <script>
  @@ -10,6 +13,7 @@ export default {
  name: 'demo-block',
  props: {
  + card: Boolean,
  title: String,
  },
  };
  @@ -28,6 +32,12 @@ export default {
  line-height: 16px;
  }
  + &__card {
  + margin: 0 12px 0;
  + overflow: hidden;
  + border-radius: 8px;
  + }
  +
  &:first-of-type {
  .van-doc-demo-block__title {
  padding-top: 20px;
  