apk: host: set lua version to 5.1 to fix help

apk: host: set lua version to 5.1 to fix help

Commit b2a84c86e3 ("apk: host: make the help available") enabled the
host build for lua (5.1) as a dependency, but apk defaults to lua 5.3.
This caused it to ignore our lua, and only build the help if the host
system had lua 5.3 installed.

Fix this by explicitly setting the lua version to ours.

Fixes: b2a84c86e3 ("apk: host: make the help available")
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>