Fix typo in picker/picker.go
Fix typo in picker/picker.go

Signed-off-by: NanXiao <11e623a37e87cf7995c466723ec99688d55cae8c@chinadtrace.org>

elifa/swarmkit,Noyan759/swarmkit,fate-grand-order/swarmkit,docker/swarmkit,jlhawn/swarmkit,elifa/swarmkit,docker/swarmkit,diogomonica/swarmkit,aaronlehmann/swarmkit,Noyan759/swarmkit,allencloud/swarmkit,fate-grand-order/swarmkit,deljuven/swarmkit,cheyang/swarmkit,yongtang/swarmkit,yp-engineering/swarmkit,vasil-yordanov/swarmkit,jlhawn/swarmkit,sungwonh/swarmkit,RenaudWasTaken/swarmkit,allencloud/swarmkit,cheyang/swarmkit,alyyousuf7/swarmkit,dperny/swarmkit-1,yongtang/swarmkit,alyyousuf7/swarmkit,cezarsa/swarmkit,aaronlehmann/swarmkit,RenaudWasTaken/swarmkit,AliyunContainerService/swarmkit,deljuven/swarmkit,dperny/swarmkit-1,yp-engineering/swarmkit,diogomonica/swarmkit,vasil-yordanov/swarmkit,cezarsa/swarmkit,sungwonh/swarmkit,AliyunContainerService/swarmkit