refactor: fix flow types

Author: posva

src/index.js

@@ -21,6 +21,8 @@ import { isRouterError, NavigationFailureType } from './util/errors'
 export default class VueRouter {
   static install: () => void
   static version: string
+  static isRouterError: Function
+  static NavigationFailureType: any
 
   app: any
   apps: Array<any>

test/unit/specs/error-handling.spec.js

@@ -1,6 +1,6 @@
 import Vue from 'vue'
 import VueRouter from '../../../src/index'
-import { NavigationFailureType } from '../../../src/history/errors'
+import { NavigationFailureType } from '../../../src/util/errors'
 
 Vue.use(VueRouter)