[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/admissionregistration/v1beta1/doc.go b/vendor/k8s.io/api/admissionregistration/v1beta1/doc.go
index 2b29efa..0a40726 100644
--- a/vendor/k8s.io/api/admissionregistration/v1beta1/doc.go
+++ b/vendor/k8s.io/api/admissionregistration/v1beta1/doc.go
@@ -15,11 +15,12 @@
 */
 
 // +k8s:deepcopy-gen=package
+// +k8s:protobuf-gen=package
 // +k8s:openapi-gen=true
 // +groupName=admissionregistration.k8s.io
 
 // Package v1beta1 is the v1beta1 version of the API.
 // AdmissionConfiguration and AdmissionPluginConfiguration are legacy static admission plugin configuration
-// InitializerConfiguration and validatingWebhookConfiguration is for the
+// MutatingWebhookConfiguration and ValidatingWebhookConfiguration are for the
 // new dynamic admission controller configuration.
 package v1beta1 // import "k8s.io/api/admissionregistration/v1beta1"