Post release: bump version string for development

Change-Id: I4aca1efa1f08c5d2ea8b492f0a6c4b9b37a54465
diff --git a/VERSION b/VERSION
index 27280b7..8207b7f 100755
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-5.3.8
+5.3.9-dev