支持SSR、升级Vue版本和增加新的icon (#40)

* search component add new style

* update vue version and support ssr

* unit test

* add new icon

* new icon

packages/image-preview/src/image-preview.js

@@ -6,12 +6,14 @@ let instance;
 const ImagePreviewConstructor = Vue.extend(ImagePreview);
 
 const initInstance = () => {
+  if (Vue.prototype.$isServer) return;
   instance = new ImagePreviewConstructor({
     el: document.createElement('div')
   });
 };
 
 var ImagePreviewBox = images => {
+  if (Vue.prototype.$isServer) return;
   if (!instance) {
     initInstance();
   }

packages/image-preview/src/image-preview.vue

@@ -2,7 +2,7 @@
   <transition name="image-fade">
     <div class="van-image-preview" ref="previewContainer" v-show="value">
       <van-swipe>
-        <van-swipe-item v-for="item in images">
+        <van-swipe-item v-for="(item, index) in images" :key="index">
           <img class="van-image-preview__image" @load="handleLoad" :src="item" alt="">
         </van-swipe-item>
       </van-swipe>