luci.mk: correct SK language name to Slovak
luci.mk: correct SK language name to Slovak

SK language code refers to Slovak, not Slovene.
Native language name is correct.

References:
https://forum.openwrt.org/viewtopic.php?id=60235
https://en.wikipedia.org/wiki/Slovak_language

Signed-off-by: Hannu Nyman <ab53a3387de93e31696058c104e6f769cd83fd1b@iki.fi>
(cherry picked from commit 1d37c9c25dbe69967a2d71495109380299974aa8)

RuiChen1113/luci,Sakura-Winkey/LuCI,Sakura-Winkey/LuCI,Sakura-Winkey/LuCI,Sakura-Winkey/LuCI,Sakura-Winkey/LuCI,db260179/openwrt-bpi-r1-luci,db260179/openwrt-bpi-r1-luci,RuiChen1113/luci,RuiChen1113/luci,RuiChen1113/luci,RuiChen1113/luci,RuiChen1113/luci,db260179/openwrt-bpi-r1-luci,Sakura-Winkey/LuCI,RuiChen1113/luci,db260179/openwrt-bpi-r1-luci,db260179/openwrt-bpi-r1-luci,RuiChen1113/luci,Sakura-Winkey/LuCI,Sakura-Winkey/LuCI,db260179/openwrt-bpi-r1-luci,db260179/openwrt-bpi-r1-luci,db260179/openwrt-bpi-r1-luci