Fix nearest_neighbor_test to compile
Fix nearest_neighbor_test to compile

kmaehashi/jubatus_core,kmaehashi/jubatus_core,kumagi/jubatus_core,gintenlabo/jubatus_core,gintenlabo/jubatus_core,kumagi/jubatus_core,rimms/jubatus_core,rimms/jubatus_core,kmaehashi/jubatus_core,kumagi/jubatus_core,kmaehashi/jubatus_core,gintenlabo/jubatus_core,gintenlabo/jubatus_core,rimms/jubatus_core,rimms/jubatus_core,kumagi/jubatus_core