message: docs(NumberKeyboard): fix multiple extraKey doc
diff: @@ -109,6 +109,7 @@ Use `title` prop to set keyboard title.
  </van-cell>
  <van-number-keyboard
  :show="show"
  + theme="custom"
  :extra-key="['00', '.']"
  close-button-text="Close"
  @blur="show = false"
  