我尝试使用以下命令在Angular-Sass项目中启用源地图：
ng serve -sm -ec
ng serve --sourcemap --extract-css
ng serve --sourcemaps=true --extract-css=true
但是，它们所有人都会产生“未知选项”错误。这些标志都不起作用。
我该如何做？
这是ng --version的输出：
Angular CLI: 7.3.0
Node: 8.9.4
OS: linux x64
Angular: 7.1.4
... animations, common, compiler, core, forms, http
... platform-browser, platform-browser-dynamic, router
Package Version
-----------------------------------------------------------
@angular-devkit/architect 0.8.9
@angular-devkit/build-angular 0.8.9
@angular-devkit/build-optimizer 0.8.9
@angular-devkit/build-webpack 0.8.9
@angular-devkit/core 0.8.9
@angular-devkit/schematics 7.3.0
@angular/cli 7.3.0
@angular/compiler-cli 7.0.4
@ngtools/webpack 6.2.9
@schematics/angular 7.3.0
@schematics/update 0.13.0
rxjs 6.4.0
typescript 3.1.6
webpack 4.16.4