[VOL-4290] Voltha go library updates for gRPC migration

Change-Id: I1aa2774beb6b7ed7419bc45aeb53fcae8a8ecda0
diff --git a/vendor/google.golang.org/protobuf/CONTRIBUTORS b/vendor/google.golang.org/protobuf/CONTRIBUTORS
new file mode 100644
index 0000000..1fbd3e9
--- /dev/null
+++ b/vendor/google.golang.org/protobuf/CONTRIBUTORS
@@ -0,0 +1,3 @@
+# This source code was written by the Go contributors.
+# The master list of contributors is in the main Go distribution,
+# visible at https://tip.golang.org/CONTRIBUTORS.