LuaWrapper: Fix comments since `ValueInRegistry` now takes an optional index
LuaWrapper: Fix comments since `ValueInRegistry` now takes an optional index

commit 28abe7558fd5c0d853a7544f49fb780aafbc49f3
Author: Remi Gacogne <8bbbac716d59f1ba632632107f33a13b2ecc97ae@powerdns.com>
Date:   Mon Dec 19 18:08:29 2016 +0100

ahupowerdns/luawrapper,ahupowerdns/luawrapper