travis: only build master branch
travis: only build master branch
campoy/golang-samples,danicat/golang-samples,adamyanliev/golang-samples,adamyanliev/golang-samples,GoogleCloudPlatform/golang-samples,campoy/golang-samples,danicat/golang-samples,campoy/golang-samples,GoogleCloudPlatform/golang-samples,adamyanliev/golang-samples,GoogleCloudPlatform/golang-samples,adamyanliev/golang-samples,danicat/golang-samples