fix(cell): vue warn "icon" was accessed (#1955)

src/packages/__VUE/cell/template.html

@@ -1,6 +1,6 @@
 <view :class="classes" :style="baseStyle" @click="handleClick">
     <slot>
-        <view class="nut-cell__icon" v-if="icon || $slots.icon">
+        <view class="nut-cell__icon" v-if="$slots.icon">
             <slot name="icon"></slot>
         </view>
         <view class="nut-cell__title" v-if="title || subTitle || $slots.title">
@@ -24,4 +24,4 @@
             <Right v-if="isLink || to" class="nut-cell__link"></Right>
         </slot>
     </slot>
-</view>
+</view>