Fix sticky pistons (#403)

Fixed method name to get the position.

mesecons_mvps/init.lua

@@ -219,7 +219,7 @@ function mesecon.mvps_move_objects(pos, dir, nodestack, movefactor)
 	movefactor = movefactor or 1
 	dir = vector.multiply(dir, movefactor)
 	for id, obj in pairs(minetest.object_refs) do
-		local obj_pos = obj:get_pos()
+		local obj_pos = obj:getpos()
 		local cbox = obj:get_properties().collisionbox
 		local min_pos = vector.add(obj_pos, vector.new(cbox[1], cbox[2], cbox[3]))
 		local max_pos = vector.add(obj_pos, vector.new(cbox[4], cbox[5], cbox[6]))