Update ruby193-rubygem-thor to 0.15.4-6.el6

- Add build support for EL6 non-SCL (dcleal@redhat.com)
- remove empty tito.props and definition which are duplicate with default from
- with recent tito you do not need SCL meta package (msuchy@redhat.com)
New package rubygem-thor, version 0.15.4-6.el6