upgrade gcp sdk version

Author: chengshifan

src/services/gcp/Dockerfile

@@ -13,7 +13,7 @@ RUN dep ensure
 RUN ./tmp/build/build.sh
 
 FROM alpine:3.7
-ENV CLOUD_SDK_VERSION 408.0.0
+ENV CLOUD_SDK_VERSION 483.0.0
 
 ENV PATH /google-cloud-sdk/bin:$PATH
 

src/services/gcp/pkg/stub/handler.go

@@ -736,10 +736,6 @@ func getExactClusterVersion(cr *v1alpha1.GKECluster, log *logrus.Entry) (string,
     }
 
     for _, c := range config.Channels {
-        if strings.ToLower(c.Channel) == "extended" {
-            // extended in not supported by --release-channel extended, see https://cloud.google.com/kubernetes-engine/docs/concepts/release-channels
-            continue
-        }
         for _, v := range c.ValidVersions {
             if strings.HasPrefix(v, cr.Spec.ClusterVersion) {
                 return v, strings.ToLower(c.Channel), nil