I was migrating from Angular version 5 to version 6. It came to my notice that angular 5 was using .angular-cli.json file whereas after migrate it to version 6 I found that that from Angular 6 version don't support .angular-cli.json file. So to make my project work I have migrated the .angular-cli.json file to angular.json. I used below command for the same.
ng update @angular/cli --from=1.7.4 --to=6 --migrate-only
Then I followed below steps.
npm cache cleannpm cache verifynpm installAfter doing above steps it worked for me.