When I used LocalePlugin in vux, I ran into a error

When I used LocalePlugin in vux, I ran into a error as followings :

> vue.esm.js?efeb:591 [Vue warn]: Property or method "$t" is not defined on the instance but referenced during render. Make sure that this property is reactive, either in the data option, or for class-based components, by initializing the property. See: https://vuejs.org/v2/guide/reactivity.html#Declaring-Reactive-Properties.
(found in )

But when I remove statement 1 and statement 2 from my code as followings, everything is OK, and language adaptor works fine. Could you please give me some advice?

```
import store from './store';
import VuexI18n from 'vuex-i18n';

import { LocalePlugin } from 'vux'; // statement 1

Vue.use(VuexI18n.plugin, store);

const vuxLocales = require('json-loader!yaml-loader!../../locales/all.yml');
const componentsLocales = require('json-loader!yaml-loader!../../locales/components.yml');

const finalLocales = {
'en': Object.assign(vuxLocales['en'], componentsLocales['en']),
'zh-CN': Object.assign(vuxLocales['zh-CN'], componentsLocales['zh-CN'])
}

for (let i in finalLocales) {
Vue.i18n.add(i, finalLocales[i])
}

Vue.use(LocalePlugin); // statement 2

Vue.i18n.set('en');
```

The relative package versions are:

"vux-loader": "^1.2.8",
"webpack": "^3.6.0",

"vue-router": "^3.0.1",
"vuex": "^3.0.1",
"vuex-i18n": "^1.10.5",
"vux": "^2.8.1",

And my webpack config is:

```
vuxLoader.merge(devWebpackConfig, {
plugins: [
'vux-ui',
{
name: 'i18n',
vuxStaticReplace: false,
staticReplace: false,
extractToFiles: 'src/locales/components.yml',
localeList: ['en','zh-CN']
}
]
}))
}
}
```