[VOL-2570]Update pyvoltha to use voltha-protos version 3.4.0

Change-Id: If43fd63ba7ae1af5aa98e022a496a24cde0e238c
diff --git a/VERSION b/VERSION
index 437459c..73462a5 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.5.0
+2.5.1