Use Ubuntu 18.04 so that a newer version of Docker will be available by default. (#12139)
Use Ubuntu 18.04 so that a newer version of Docker will be available by default. (#12139)


ray-project/ray,richardliaw/ray,ray-project/ray,richardliaw/ray,pcmoritz/ray-1,ray-project/ray,richardliaw/ray,richardliaw/ray,pcmoritz/ray-1,ray-project/ray,pcmoritz/ray-1,ray-project/ray,pcmoritz/ray-1,ray-project/ray,richardliaw/ray,ray-project/ray,richardliaw/ray,pcmoritz/ray-1,pcmoritz/ray-1,richardliaw/ray,pcmoritz/ray-1,richardliaw/ray,pcmoritz/ray-1,ray-project/ray