Update OpenHashSet.scala

Modify wrong comment of function addWithoutResize.

Author: ArcherShao <ArcherShao@users.noreply.github.com>

Closes #667 from ArcherShao/patch-3 and squashes the following commits:

a607358 [ArcherShao] Update OpenHashSet.scala

(cherry picked from commit 0a5a46811475a7accac1ed8dfefeeba9554456db)
Signed-off-by: Reynold Xin <rxin@apache.org>