Step(doc): fix doc

examples/docs/steps.md

@@ -1,3 +1,19 @@
+<script>
+  export default {
+    data() {
+      return {
+        active: 0
+      };
+    },
+
+    methods: {
+      next() {
+        if (this.active++ > 2) this.active = 0;
+      }
+    }
+  }
+</script>
+
 ## Steps 步骤条
 引导用户按照流程完成任务的分步导航条，可根据实际应用场景设定步骤，步骤不得少于2步