Run luacheck and fix warnings.

Update `lastMove` instead of redefine.

.luacheckrc

@@ -0,0 +1,7 @@
+unused_args = false
+allow_defined_top = true
+
+read_globals = {
+	"minetest",
+	"default",
+}

init.lua

@@ -504,9 +504,9 @@ function realchess.move(pos, from_list, from_index, to_list, to_index, _, player
 
 	meta:set_string("playerWhite", playerWhite)
 	meta:set_string("playerBlack", playerBlack)
-	meta:set_string("lastMove", thisMove)
+	lastMove = thisMove
+	meta:set_string("lastMove", lastMove)
 	meta:set_int("lastMoveTime", minetest.get_gametime())
-	local lastMove = meta:get_string("lastMove")
 
 	if lastMove == "black" then
 		minetest.chat_send_player(playerWhite, "["..os.date("%H:%M:%S").."] "..