build: Really bump vala requirement to 0.18
build: Really bump vala requirement to 0.18

Pelagicore/Media-Manager-Rygel-patched,Tarnyko/rygel,jku/rygel,GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched,jku/rygel,GNOME/rygel,GNOME/rygel,Tarnyko/rygel,Pelagicore/Media-Manager-Rygel-patched