`is_writable` should be out of `util`
`is_writable` should be out of `util`

kumagi/jubatus_core,gintenlabo/jubatus_core,roselleebarle04/jubatus,kumagi/jubatus_core,mathn/jubatus,rimms/jubatus_core,Asuka52/jubatus,gintenlabo/jubatus,jubatus/jubatus,elkingtonmcb/jubatus,jubatus/jubatus,elkingtonmcb/jubatus,rimms/jubatus_core,kmaehashi/jubatus,rimms/jubatus,kumagi/jubatus_core,gintenlabo/jubatus,kmaehashi/jubatus_core,kmaehashi/jubatus_core,Asuka52/jubatus,rimms/jubatus_core,gintenlabo/jubatus_core,rimms/jubatus_core,kmaehashi/jubatus_core,jubatus/jubatus,roselleebarle04/jubatus,kmaehashi/jubatus_core,kmaehashi/jubatus,gintenlabo/jubatus_core,mathn/jubatus,gintenlabo/jubatus_core,rimms/jubatus,kumagi/jubatus_core