chore: replace @angular-devkit/core with @ngtools/webpack

Author: sis0k0

demo-angular/package.json

@@ -40,6 +40,6 @@
     "nativescript-dev-typescript": "~0.7.0",
     "nativescript-dev-webpack": "~0.14.0",
     "typescript": "~2.7.2",
-    "@angular-devkit/build-angular": "~0.7.0-rc.0"
+    "@ngtools/webpack": "~6.1.0-rc.0"
   }
-}
+}