Update libts-lua.lua

src/util/libts-lua.lua

@@ -134,7 +134,7 @@ end
 
 ---@diagnostic disable-next-line: duplicate-set-field
 function io.lines(fn)
-	local fi, err, fn2 = io.open(fn, nil, 2)
+	local fi, err, fn2 = io.open(fn, 'r', 2)
 	if not fi then error('Error opening file \''..fn2..'\': '..err, 2) end
 	return fi:lines()
 end