Fix unhashable type

Change-Id: I6610d98e16d5d30347b82b58ea195668ad3e1491
diff --git a/jenkins/client/job/git-mirrors/upstream.yml b/jenkins/client/job/git-mirrors/upstream.yml
index 92766ea..bb94171 100644
--- a/jenkins/client/job/git-mirrors/upstream.yml
+++ b/jenkins/client/job/git-mirrors/upstream.yml
@@ -27,7 +27,7 @@
             trigger:
               gerrit:
                 project:
-                  {{downstream}}:
+                  "{{downstream}}":
                     branches:
                       - master
                 message: