I was having the same problem today and I fixed it by:
- delete the tree-kill package from the node_modules folder.
- delete the package-lock.json file.
- go to the @angular-devkit/build-angular folder in the node_modules folder and edit the package.json file; change tree-kill version from 1.2.1 to 1.2.2
- go to @ngtools/webpack folder in the node_modules folder and do the same as step 3.
run npm install after that.