Fix warning reported by LuaCheck (#563)

David Leal

2020-09-05 11f2b4f4b317a25972733e3d3fe9f2dc6ce31c6a

 technic/tools/mining_lasers.lua

@@ -46,7 +46,7 @@
      })
      return
   end
   minetest.node_dig(pos, node, player)
   def.on_dig(pos, node, player)
end

local keep_node = {air = true}