title: Vuex modules - cannot set the ..mapGetters correvctly
body: <p>I currently defined my store structure as following</p>
  
  <pre><code>store
    modules
      User.js
   index.js
  </code></pre>
  
  <p>store/modules/User.js</p>
  
  <pre><code>import * as types from '@/store/mutation_types'
  import firebase from 'firebase'
  
  const state = {
    ...
    user: JSON.parse(localStorage.getItem('user')) || null
  }
  
  const actions = {
    setUser ({commit}, newUser) {
      console.log('STORE ACTION setUser: ', newUser)
      commit(types.SET_USER, newUser)
    },
    signUserIn ({commit}, payload) {
      ...
    },
    signUserUp ({commit}, payload) {
      ...
    },
    logout: context =&gt; {
     ...
    }
  }
  
  const mutations = {
   ...
  }
  
  const getters = {
    ...
    user: state =&gt; state.user
  }
  
  export const User = {
    namespaced: true,
    state,
    actions,
    mutations,
    getters
  }
  </code></pre>
  
  <p>store/index.js</p>
  
  <pre><code>/**
   * Import Dependency
   */
  import Vue from 'vue'
  import Vuex from 'vuex'
  import { firebaseMutations } from 'vuexfire'
  import * as types from '@/store/mutation_types'
  import { User } from '@/store/modules/User.js'
  import { Account } from '@/store/modules/Account.js'
  
  Vue.use(Vuex)
  
  const store = new Vuex.Store({
    strict: process.env.NODE_ENV !== 'production',
    state: {
      language: localStorage.getItem('language') || '',
      ...
    },
    actions: {
      switchLanguage ({ commit }, context) {
        commit(types.SET_LANGUAGE, context)
      },
      ...
    },
    getters: {
      language: state =&gt; state.language,
      sideNav: state =&gt; state.sideNav,
      showAssociation: state =&gt; state.showAssociation,
      ...
    },
    mutations: {
      ...
      },
      ...firebaseMutations
    },
    modules: {
      User,
      Account
    }
  })
  
  export default store
  </code></pre>
  
  <p>In a component , I need to use ..mapGetters from teh User module AND from the index.js</p>
  
  <p>...mapGetters('User', ['user'], ['sideNav', 'showAssociation']),</p>
  
  <p>BUT this is not right ...  I get an error :</p>
  
  <pre><code> Property or method "showAssociation" is not defined
  </code></pre>
  
  <p>How should I write my ...mapGetters ?
  or is it anything wrng in my User module ?</p>
  
  <p>thanks for feedback</p>