Update licence year as range
Update licence year as range

From https://www.gnu.org/licenses/gpl-howto.html,

> copyright notice should include the year in which you finished
preparing the release

> For software with several releases over multiple years, it's okay to
use a range (“2008-2010”)

nelsonghezzi/spaceship-zsh-theme,denysdovhan/spaceship-zsh-theme