Fix compilation error on CentOS. (#622)
Fix compilation error on CentOS. (#622)

* Fix compilation error on CentOS.

* add TODO

pcmoritz/ray-1,Wapaul1/ray,ujvl/ray-ng,atumanov/ray,richardliaw/ray,Wapaul1/ray,robertnishihara/ray,ray-project/ray,alanamarzoev/ray,richardliaw/ray,pcmoritz/ray-1,stephanie-wang/ray,atumanov/ray,stephanie-wang/ray,stephanie-wang/ray,Wapaul1/ray,stephanie-wang/ray,robertnishihara/ray,ray-project/ray,ray-project/ray,alanamarzoev/ray,richardliaw/ray,atumanov/ray,atumanov/ray,robertnishihara/ray,richardliaw/ray,Wapaul1/ray,stephanie-wang/ray,pcmoritz/ray-1,alanamarzoev/ray,atumanov/ray,ujvl/ray-ng,ray-project/ray,robertnishihara/ray,ray-project/ray,stephanie-wang/ray,stephanie-wang/ray,ujvl/ray-ng,stephanie-wang/ray,ray-project/ray,alanamarzoev/ray,atumanov/ray,pcmoritz/ray-1,richardliaw/ray,Wapaul1/ray,robertnishihara/ray,Wapaul1/ray,ray-project/ray,stephanie-wang/ray,atumanov/ray,robertnishihara/ray,richardliaw/ray,pcmoritz/ray-1,pcmoritz/ray-1,robertnishihara/ray,pcmoritz/ray-1,pcmoritz/ray-1,atumanov/ray,alanamarzoev/ray,richardliaw/ray,ujvl/ray-ng,richardliaw/ray,alanamarzoev/ray,robertnishihara/ray,robertnishihara/ray,ray-project/ray