Use voltha-protos version 4.0.2
Bump major version of voltha-lib-go to 4.0.0 as this change results
in incompatible API version compared to previous version

Change-Id: I1def58361fb1d85f07d6948ebf1ffb7a92eb0d4c
diff --git a/pkg/db/backend.go b/pkg/db/backend.go
index efc0953..d6867a5 100644
--- a/pkg/db/backend.go
+++ b/pkg/db/backend.go
@@ -23,8 +23,8 @@
 	"sync"
 	"time"
 
-	"github.com/opencord/voltha-lib-go/v3/pkg/db/kvstore"
-	"github.com/opencord/voltha-lib-go/v3/pkg/log"
+	"github.com/opencord/voltha-lib-go/v4/pkg/db/kvstore"
+	"github.com/opencord/voltha-lib-go/v4/pkg/log"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
 )