message: docs(Checkbox): fix model-value prop
diff: </demo-block>
  <demo-block :title="t('disabled')">
  - <van-checkbox :value="false" disabled>
  + <van-checkbox :model-value="false" disabled>
  {{ t('checkbox') }}
  </van-checkbox>
  - <van-checkbox :value="true" disabled>
  + <van-checkbox :model-value="true" disabled>
  {{ t('checkbox') }}
  </van-checkbox>
  </demo-block>
  