[Improvement] Support Vue.use to register a component (#401)

packages/step/index.vue

@@ -2,7 +2,7 @@
   <div class="van-step van-hairline" :class="[`van-step--${$parent.direction}`, { [`van-step--${status}`]: status }]">
     <div class="van-step__circle-container">
       <i class="van-step__circle" v-if="status !== 'process'" />
-      <i class="van-icon van-icon-checked" :style="{ color: $parent.activeColor }" v-else />
+      <icon v-else name="checked" :style="{ color: $parent.activeColor }" />
     </div>
     <div class="van-step__title" :style="titleStyle">
       <slot></slot>
@@ -12,7 +12,9 @@
 </template>
 
 <script>
-export default {
+import { create } from '../utils';
+
+export default create({
   name: 'van-step',
 
   beforeCreate() {
@@ -37,5 +39,5 @@ export default {
       } : {};
     }
   }
-};
+});
 </script>