build: update minimum meson_version to 0.59.0

That fixes following build warning:

$ meson . _build
...
WARNING: Project specifies a minimum meson_version '>= 0.56.0' but uses features which were added in newer versions:
 * 0.57.0: {'gnome.post_install'}
 * 0.59.0: {'update_desktop_database arg in gnome.post_install'}