Update version for 1.5.0-rc1

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/VERSION b/VERSION
index 245205d..8d9b8b2 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.4.90
+1.4.91