修复：picker中值变了后未更新picker-colum中的值 (#23)

* 修复：picker中值变了后未更新picker-colum中的值

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

@@ -16,6 +16,7 @@ var ImagePreviewBox = images => {
     initInstance();
   }
 
+  /* istanbul ignore else */
   if (!instance.value) {
     instance.images = images;
 

packages/picker/src/picker-column.vue

@@ -69,10 +69,14 @@ export default {
       this.currentValues = val;
     },
     currentValues(val) {
+      /* istanbul ignore else */
       if (this.valueIndex === -1) {
         this.currentValue = (val || [])[0];
       }
     },
+    value(val) {
+      this.currentValue = val;
+    },
     currentValue(val) {
       this.doOnValueChange();