[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/kubernetes/typed/events/v1beta1/events_client.go b/vendor/k8s.io/client-go/kubernetes/typed/events/v1beta1/events_client.go
index fb59635..e372ccf 100644
--- a/vendor/k8s.io/client-go/kubernetes/typed/events/v1beta1/events_client.go
+++ b/vendor/k8s.io/client-go/kubernetes/typed/events/v1beta1/events_client.go
@@ -20,7 +20,6 @@
 
 import (
 	v1beta1 "k8s.io/api/events/v1beta1"
-	serializer "k8s.io/apimachinery/pkg/runtime/serializer"
 	"k8s.io/client-go/kubernetes/scheme"
 	rest "k8s.io/client-go/rest"
 )
@@ -71,7 +70,7 @@
 	gv := v1beta1.SchemeGroupVersion
 	config.GroupVersion = &gv
 	config.APIPath = "/apis"
-	config.NegotiatedSerializer = serializer.DirectCodecFactory{CodecFactory: scheme.Codecs}
+	config.NegotiatedSerializer = scheme.Codecs.WithoutConversion()
 
 	if config.UserAgent == "" {
 		config.UserAgent = rest.DefaultKubernetesUserAgent()