Documentation: HOWTO: update versions from 3.x to 4.x

Versions in HOWTO was updated to 4.x by commit
e4144fe5 ("docs: update HOWTO for 3.x ->
4.x versioning") but not applied to Korean translation. This commit
apply the change.

Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>