[VOL-1866] Changed module dependency to v12.0.0 of k8s client-go and v1.15.4 of k8s api/apimachinery in sync with other voltha components

Had to use pseudo-version corresponding to v12.0.0 of k8s client-go
because golang proxy is no longer serving the modules not complying
to Semantic Import Versioning rules including client-go v12.0.0.
Refer to https://github.com/kubernetes/client-go/issues/631 and
https://github.com/golang/go/issues/33558

Change-Id: I2e558bab7f0702f230761319eb5392a7d0532ea3
diff --git a/vendor/k8s.io/api/rbac/v1alpha1/doc.go b/vendor/k8s.io/api/rbac/v1alpha1/doc.go
index f2547a5..918b8a3 100644
--- a/vendor/k8s.io/api/rbac/v1alpha1/doc.go
+++ b/vendor/k8s.io/api/rbac/v1alpha1/doc.go
@@ -15,6 +15,7 @@
 */
 
 // +k8s:deepcopy-gen=package
+// +k8s:protobuf-gen=package
 // +k8s:openapi-gen=true
 
 // +groupName=rbac.authorization.k8s.io