message: fix(list): fix loading-text support
diff: <div v-show="loading" :class="b('loading')">
  <slot name="loading">
  <loading />
  - <span :class="b('loading-text')">{{ $t('loadingTip') }}</span>
  + <span :class="b('loading-text')">{{ loadingText || $t('loadingTip') }}</span>
  </slot>
  </div>
  </div>
  @@ -32,7 +32,8 @@ export default create({
  offset: {
  type: Number,
  default: 300
  - }
  + },
  + loadingText: String
  },
  mounted() {
  