Fix warning reported by LuaCheck (#563)

David Leal

2020-09-05 11f2b4f4b317a25972733e3d3fe9f2dc6ce31c6a

 technic/machines/register/machine_base.lua

@@ -38,7 +38,7 @@
   local machine_desc = data.machine_desc
   local tier = data.tier
   local ltier = string.lower(tier)
	

   data.modname = data.modname or minetest.get_current_modname()

   local groups = {cracky = 2, technic_machine = 1, ["technic_"..ltier] = 1}