(Angular) Error - You can check this with `npm ls @ngtools/webpack`, and then remove the extra copies. 해결법

○ ng build 또는 ng serve시 에러

ERROR in ./src/polyfills.ts

Module build failed: Error: Angular Compiler was detected but it was an instance of the wrong class.

This likely means you have several @ngtools/webpack packages installed. You can check this with `npm ls @ngtools/webpack`, and then remove the extra copies.

○ npm ls @ngtools/webpack 입력

+-- @angular/cli@1.6.3

| `-- @ngtools/webpack@1.9.3

`-- @ngtools/webpack@1.10.2

○ 해결방법

1.

rm -rf node_modules

2.

rm -rf package-lock.json

3.

npm cache clean -f

4.

npm install

5.

ng build

npm start

정상 동작!!