fix(app): better fix for usmin path problem

Replaces:
yeoman/generator-angular@27dd848f58c45ba5536da502bfd5a147ced35572

@eddiemonge: Hi, as @lazarrs mentioned in https://github.com/yeoman/generator-angular/issues/728, i also think this is a much better solution to fix the usmin paths as in my last PR, do you agree?