Currently, I have an Angular 2 project folder with a separate service folder named "auth.service.ts" located outside of it. Within this service file, I am importing `Injectable` from `@angular/core`. However, due to the service being located outside of the main Angular project folder, I am receiving an error stating that it cannot find the module '@angular/core'. Does anyone have any suggestions on how to resolve this issue while still keeping the service file outside of the main folder?