Post release: bump version string for development

Change-Id: I981c03eb32b5fe76b150b10d3c62530cc1325bef
diff --git a/VERSION b/VERSION
index cdb98d2..4de34c3 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-5.1.3
+5.1.4-dev