Build 'quota' master against Gerrit 'stable-3.8' branch

Change-Id: I27d974d3e10776c1f18a625e527cdae069a0664d
diff --git a/jenkins/gerrit-bazel-plugin-quota.yaml b/jenkins/gerrit-bazel-plugin-quota.yaml
index 6090b78..212dee3 100644
--- a/jenkins/gerrit-bazel-plugin-quota.yaml
+++ b/jenkins/gerrit-bazel-plugin-quota.yaml
@@ -7,6 +7,7 @@
             - master
           gerrit-branch:
             - master
+            - stable-3.8
             - stable-3.7
             - stable-3.6
             - stable-3.5