cgroup's document path is changed to "cgroup-v1".  update it.

Link: http://lkml.kernel.org/r/1470322507-5161-1-git-send-email-iamyooon@gmail.comSigned-off-by: Nseokhoon.yoon <iamyooon@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>