Bumping version after 2.7 release

Change-Id: I6beb119ac996fc89630023c4ac56dfe958fb8230
diff --git a/VERSION b/VERSION
index 4cda8f1..bcfbf47 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.5.2
+1.6.0-dev