fix memory leak
fix memory leak

kamigaito/cnn,mitchellstern/dynet,yoavg/cnn,kaishengyao/cnn,kaishengyao/cnn,cherryc/dynet,Peilun-Li/dynet,yanweifu/cnn,dhgarrette/cnn,Aureliu/cnn,echohenry2006/cnn,mitchellstern/dynet,cherryc/dynet,Abasyoni/dynet,zhangscth/cnn,Abasyoni/dynet,dhgarrette/cnn,Peilun-Li/dynet,Peilun-Li/dynet,dhgarrette/cnn,mrzu/cnn,ndnlp/cnn,yoavg/cnn,Abasyoni/dynet,cherryc/dynet,kamigaito/cnn