bump version to 17.09.0-ce-rc1

Signed-off-by: Eli Uriegas <eli.uriegas@docker.com>
diff --git a/VERSION b/VERSION
index 2d736aa..79142b0 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-17.06.0-dev
+17.09.0-ce-rc1