[Improvement] Layout: support flex (#1305)

packages/col/index.vue

@@ -1,11 +1,11 @@
 <template>
-  <div
-    class="van-col"
-    :class="{ [`van-col-${span}`]: span, [`van-col-offset-${offset}`]: offset}"
+  <component
+    :is="tag"
+    :class="b({ [span]: span, [`offset-${offset}`]: offset })"
     :style="style"
   >
     <slot />
-  </div>
+  </component>
 </template>
 
 <script>
@@ -16,7 +16,11 @@ export default create({
 
   props: {
     span: [Number, String],
-    offset: [Number, String]
+    offset: [Number, String],
+    tag: {
+      type: String,
+      default: 'div'
+    }
   },
 
   computed: {