docs(README.md) adjust go version to build etcd-ca
docs(README.md) adjust go version to build etcd-ca

kingoftowns/etcd-ca,endocode/etcd-ca,endocode/etcd-ca,coreos/etcd-ca,coreos/etcd-ca,oscarrr110/etcd-ca,kingoftowns/etcd-ca,hzy001/etcd-ca,hzy001/etcd-ca,oscarrr110/etcd-ca