Update DEVSTACK_SERIES to stein

stable/rocky branch has been created now and
current master is for stein.

Change-Id: Id5d75e7a8a38a749f387f3ba670e3d2c10cb9719
diff --git a/stackrc b/stackrc
index 2088bf4..34bd677 100644
--- a/stackrc
+++ b/stackrc
@@ -258,7 +258,7 @@
 # Setting the variable to 'ALL' will activate the download for all
 # libraries.
 
-DEVSTACK_SERIES="rocky"
+DEVSTACK_SERIES="stein"
 
 ##############
 #