安装 Vuetify 后，我目前收到以下控制台错误。我正在使用 webpack v3.6
Uncaught TypeError: Cannot read property 'extend' of undefined
at Module../src/mixins/themeable/index.ts (index.ts:21)
at __webpack_require__ (bootstrap:19)
at Module../src/components/VApp/VApp.ts (vuetify.js:391)
at __webpack_require__ (bootstrap:19)
at Module../src/components/VApp/index.ts (index.ts:1)
at __webpack_require__ (bootstrap:19)
at Module../src/components/index.ts (index.ts:1)
at __webpack_require__ (bootstrap:19)
at Module../src/index.ts (vuetify.js:32032)
at __webpack_require__ (bootstrap:19)
./src/mixins/themeable/index.ts @ index.ts:21
__webpack_require__ @ bootstrap:19
./src/components/VApp/VApp.ts @ vuetify.js:391
__webpack_require__ @ bootstrap:19
./src/components/VApp/index.ts @ index.ts:1
__webpack_require__ @ bootstrap:19
./src/components/index.ts @ index.ts:1
__webpack_require__ @ bootstrap:19
./src/index.ts @ vuetify.js:32032
__webpack_require__ @ bootstrap:19
(anonymous) @ bootstrap:83
(anonymous) @ bootstrap:83
webpackUniversalModuleDefinition …