[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/client-go/pkg/apis/clientauthentication/OWNERS b/vendor/k8s.io/client-go/pkg/apis/clientauthentication/OWNERS
index 3b7ea1b..e0ec62d 100644
--- a/vendor/k8s.io/client-go/pkg/apis/clientauthentication/OWNERS
+++ b/vendor/k8s.io/client-go/pkg/apis/clientauthentication/OWNERS
@@ -1,3 +1,5 @@
+# See the OWNERS docs at https://go.k8s.io/owners
+
 # approval on api packages bubbles to api-approvers
 reviewers:
 - sig-auth-authenticators-approvers
diff --git a/vendor/k8s.io/client-go/pkg/apis/clientauthentication/v1alpha1/types.go b/vendor/k8s.io/client-go/pkg/apis/clientauthentication/v1alpha1/types.go
index 921f3a2..c714e24 100644
--- a/vendor/k8s.io/client-go/pkg/apis/clientauthentication/v1alpha1/types.go
+++ b/vendor/k8s.io/client-go/pkg/apis/clientauthentication/v1alpha1/types.go
@@ -22,7 +22,7 @@
 
 // +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object
 
-// ExecCredentials is used by exec-based plugins to communicate credentials to
+// ExecCredential is used by exec-based plugins to communicate credentials to
 // HTTP transports.
 type ExecCredential struct {
 	metav1.TypeMeta `json:",inline"`