Releasing version 6.0.0 for voltha 2.6

Change-Id: If47b18ba2bd5c650034ec032c4b3699df81f6e73
diff --git a/VERSION b/VERSION
index f547a37..09b254e 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-5.1.7-dev
+6.0.0