monitoring/listresources: fix metric type
monitoring/listresources: fix metric type

Change-Id: Id8f22a91d1e896ac582b8d06477469f7530ef357

GoogleCloudPlatform/golang-samples,GoogleCloudPlatform/golang-samples,adamyanliev/golang-samples,campoy/golang-samples,adamyanliev/golang-samples,danicat/golang-samples,danicat/golang-samples,campoy/golang-samples,adamyanliev/golang-samples,adamyanliev/golang-samples,danicat/golang-samples,GoogleCloudPlatform/golang-samples,campoy/golang-samples