sandbox: update Lua version assert for Lua 5.3
sandbox: update Lua version assert for Lua 5.3

See https://travis-ci.org/starius/lua-npge/jobs/52587337#L776

npge/lua-npge,starius/lua-npge,npge/lua-npge,starius/lua-npge,starius/lua-npge,npge/lua-npge