🐛 bug(mixin): fix memory leak

closes kazupon#514

Author: kazupon

src/index.js

@@ -130,6 +130,10 @@ export default class VueI18n {
     Vue.config.silent = silent
   }
 
+  destroyVM (): void {
+    this._vm.$destroy()
+  }
+
   subscribeDataChanging (vm: any): void {
     this._dataListeners.push(vm)
   }

src/mixin.js

@@ -95,6 +95,7 @@ export default {
 
       if (self._i18nWatcher) {
         self._i18nWatcher()
+        self._i18n.destroyVM()
         delete self._i18nWatcher
       }