Update Kodi-Headless to latest (Leia 18.4)

Hello,

Leia 18.4 was released earlier this month but the latest image published to Docker Hub is still 18.3. When you get a chance, could you look into updating the latest image? I updated my non headless apps earlier this week and then realized that there was a mismatch (hopefully this won’t cause any issues in the interim).

Appreciate it!