<script src="https://unpkg.com/vue-router/dist/vue-router.js"></script>cdn 주소를 쓰고 있었는데 갑자기 안됬음
https://v3.router.vuejs.org/installation.html
홈페이지에도 잘못 기재 되있는거 같음 (v3.x)
<script src="https://unpkg.com/vue-router@3"></script>이걸로 하니까 됨..
버전 4는 https://unpkg.com/vue-router@4
