Bump minor version post VOLTHA2.4 branch out

Change-Id: Ic7cf02790d718e48a5b08ff8407ffbec7f16d500
diff --git a/VERSION b/VERSION
index 3b47f2e..688932a 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-3.3.9
+3.4.0-dev