[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/settings/v1alpha1/generated.proto b/vendor/k8s.io/api/settings/v1alpha1/generated.proto
index d5534c4..db1ec93 100644
--- a/vendor/k8s.io/api/settings/v1alpha1/generated.proto
+++ b/vendor/k8s.io/api/settings/v1alpha1/generated.proto
@@ -42,7 +42,7 @@
 // PodPresetList is a list of PodPreset objects.
 message PodPresetList {
   // Standard list metadata.
-  // More info: https://git.k8s.io/community/contributors/devel/api-conventions.md#metadata
+  // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
   // +optional
   optional k8s.io.apimachinery.pkg.apis.meta.v1.ListMeta metadata = 1;