fixing test error (https://github.com/daumkakao/s2graph/issues/10)
fixing test error (https://github.com/daumkakao/s2graph/issues/10)

jongwook/incubator-s2graph,SteamShon/incubator-s2graph,daewon/incubator-s2graph,SteamShon/incubator-s2graph,jongwook/incubator-s2graph,SteamShon/incubator-s2graph,daewon/incubator-s2graph