I was also getting this issue and solved by running below command.
ng update @angular/cli --migrate-only --from=<WhateverVersionYouAreCurrentlyOn>
e.g.
ng update @angular/cli --migrate-only --from=1.7.3
getting ref from here
I was also getting this issue and solved by running below command.
ng update @angular/cli --migrate-only --from=<WhateverVersionYouAreCurrentlyOn>
e.g.
ng update @angular/cli --migrate-only --from=1.7.3
getting ref from here