Vue component lists rendered with v-for should have explicit keys

I'm trying to build a small application on VueJS with using Vue-grid-layout package. I created a component file named pageBuilder.vue and added following contents:

<template>
    <div>
        <grid-layout
                :layout="layout"
                :col-num="16"
                :row-height="30"
                :is-draggable="true"
                :is-resizable="true"
                :vertical-compact="true"
                :margin="[10, 10]"
                :use-css-transforms="true"
        >
            <grid-item class="grid-cell" v-for="item in layout"
                       :x="item.x"
                       :y="item.y"
                       :w="item.w"
                       :h="item.h"
                       :i="item.i">
                <button @click="click">
                    Click
                </button>
            </grid-item>
        </grid-layout>
    </div>
</template>

<script>
    import * as VueGridLayout from "vue-grid-layout";
    var GridLayout = VueGridLayout.GridLayout;
    var GridItem = VueGridLayout.GridItem;
    export default {
        name: "page-builder",
        components: {
            GridLayout, GridItem
        },
        data() {
            return {
                layout: [{
                    "x": 0,
                    "y": 0,
                    "w": 4,
                    "h": 2,
                    "i": "0"
                }, {
                    "x": 4,
                    "y": 0,
                    "w": 4,
                    "h": 4,
                    "i": "1"
                }],
            }
        },
        methods: {
            click: function(){
                alert('clicked')
            }
        }
    }
</script>

<style scoped>

</style>

I followed the following example to implement the package. But I'm am getting warning messages

(Emitted value instead of an instance of Error) : component lists rendered with v-for should have explicit keys. See https://vuejs.org/guide/list.ht ml#key for more info.

Error screenshot

I am binding the values but still getting warning messages, help me out in this. Thanks.