update dmlc-core
update dmlc-core

crazy-cat/incubator-mxnet,crazy-cat/incubator-mxnet,crazy-cat/incubator-mxnet,crazy-cat/incubator-mxnet,crazy-cat/incubator-mxnet,crazy-cat/incubator-mxnet,crazy-cat/incubator-mxnet,crazy-cat/incubator-mxnet,crazy-cat/incubator-mxnet