修复Loadmore的transform样式导致的Popup定位错误

packages/loadmore/src/loadmore.vue

 <template>
   <div class="mint-loadmore">
-    <div class="mint-loadmore-content" :class="{ 'is-dropped': topDropped || bottomDropped}" :style="{ 'transform': 'translate3d(0, ' + translate + 'px, 0)' }">
+    <div class="mint-loadmore-content" :class="{ 'is-dropped': topDropped || bottomDropped}" :style="{ 'transform': transform }">
       <slot name="top">
         <div class="mint-loadmore-top" v-if="topMethod">
           <spinner v-if="topStatus === 'loading'" class="mint-loadmore-spinner" :size="20" type="fading-circle"></spinner>
@@ -140,6 +140,12 @@
       };
     },
 
+    computed: {
+      transform() {
+        return this.translate === 0 ? null : 'translate3d(0, ' + this.translate + 'px, 0)';
+      }
+    },
+
     watch: {
       topStatus(val) {
         this.$emit('top-status-change', val);