bump to 17.05.0-rc1

Signed-off-by: Victor Vieux <victorvieux@gmail.com>
diff --git a/VERSION b/VERSION
index 0c1492a..c3337a2 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-17.05.0-dev
+17.05.0-ce-rc1