vuex载入vue时store首字母不可大写

在一次使用vuex中突然报以下错误

TypeError: Cannot read property 'commit' of undefined
    at VueComponent.mappedMutation (vuex.esm.js?ed0c:906)
    at VueComponent.selectSinger (search-suggest.vue?adea:110)
    at click (eval at ./node_modules/vue-loader/lib/template-compiler/index.js?{"id":"data-v-51f1ca22","hasScoped":true,"transformToRequire":{"video":["src","poster"],"source":"src","img":"src","image":"xlink:href"},"buble":{"transforms":{}}}!./node_modules/vue-loader/lib/selector.js?type=template&index=0!./src/components/search-suggest.vue (app.js:1722), <anonymous>:29:32)
    at invokeWithErrorHandling (vue.esm.js?efeb:1863)
    at HTMLDivElement.invoker (vue.esm.js?efeb:2188)
    at HTMLDivElement.original._wrapper (vue.esm.js?efeb:7565)
    at click (bscroll.esm.js?fd05:352)
    at BScroll._checkClick (bscroll.esm.js?fd05:1347)
    at BScroll._end (bscroll.esm.js?fd05:1222)
    at BScroll.handleEvent (bscroll.esm.js?fd05:785)

看了一下代码是这样的

import Store from './store'
import Vue from "vue"
let app = new Vue({
  el:"#app",
  render:(a)=>a(App),
  Store,
})

把store首字母改小写后不报错

import store from './store'
import Vue from "vue"
let app = new Vue({
  el:"#app",
  render:(a)=>a(App),
  store,
})