monitoring/custommetric: fix typo (#281)
monitoring/custommetric: fix typo (#281)


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