bump version to 17.10.0-ce-rc1

Signed-off-by: Andrew Hsu <andrewhsu@docker.com>
diff --git a/VERSION b/VERSION
index 2d736aa..c796782 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-17.06.0-dev
+17.10.0-ce-rc1