Makefile: Fix generating source-map with webpack
Makefile: Fix generating source-map with webpack

The command is slightly different to really get source maps for the `ng-admin.min.js` and `ng-admin.min.css` files.
LuckeyHomes/ng-admin,LuckeyHomes/ng-admin,ulrobix/ng-admin,marmelab/ng-admin,LuckeyHomes/ng-admin,marmelab/ng-admin,marmelab/ng-admin,ulrobix/ng-admin,ulrobix/ng-admin