bump version to 17.10.0-ce-rc2

Signed-off-by: Andrew Hsu <andrewhsu@docker.com>
diff --git a/VERSION b/VERSION
index c796782..f045786 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-17.10.0-ce-rc1
+17.10.0-ce-rc2