[improvement] avoid use cell selector (#2714)

packages/contact-list/index.js

@@ -23,6 +23,8 @@ export default sfc({
       <Cell
         key={item.id}
         isLink
+        class={bem('item')}
+        value-class={bem('item-value')}
         scopedSlots={{
           default: () => (
             <Radio name={item.id}>

packages/contact-list/index.less

@@ -5,11 +5,11 @@
   padding-bottom: 50px;
   box-sizing: border-box;
 
-  .van-cell {
+  &__item {
     padding: 15px;
   }
 
-  .van-cell__value {
+  &__item-value {
     color: @text-color;
     padding-right: 34px;
     position: relative;