Bumping VERSION to 2.7.0-dev after 2.6.0 release

Change-Id: Ib3d0be121515579c9707b715fe917e9d62d6833a
diff --git a/VERSION b/VERSION
index e70b452..6886b8a 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.6.0
+2.7.0-dev