김정환님 글 : https://jeonghwan-kim.github.io/2018/05/31/vue-form-validation.html
공식 문서 : https://kr.vuejs.org/v2/cookbook/form-validation.html
이메일 검증 스택오버플로우 : https://stackoverflow.com/questions/46155/how-to-validate-an-email-address-in-javascript
