fix subject line

Change-Id: I0fcab929b93567a98d8b9fefeec22cc8a718a59a
diff --git a/Jenkinsfile b/Jenkinsfile
index 2751835..6b773df 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -93,7 +93,7 @@
         }
 
         mail to: env.recipients,
-            subject: branch + ' released',
+            subject: metadata['release_version'] + ' released',
             replyTo: 'cord-discuss@opencord.org',
             body: '''Hi CORD Community,