Build github plugin on stable-3.3

Change-Id: If856bb34ab8562f6070157ad3dd1d7c73143b3a3
diff --git a/jenkins/gerrit-mvn-plugin-github.yaml b/jenkins/gerrit-mvn-plugin-github.yaml
index cd75d14..936d343 100644
--- a/jenkins/gerrit-mvn-plugin-github.yaml
+++ b/jenkins/gerrit-mvn-plugin-github.yaml
@@ -3,6 +3,7 @@
     repo: github
     branch:
       - master
+      - stable-3.3
       - stable-3.2
       - stable-3.1
       - stable-3.0