Build github plugin on stable-3.4 branch

Change-Id: Ib889ff3c4eb0bd35d58dad8169d7a488284b46e7
diff --git a/jenkins/gerrit-mvn-plugin-github.yaml b/jenkins/gerrit-mvn-plugin-github.yaml
index f6e9918..03a5c82 100644
--- a/jenkins/gerrit-mvn-plugin-github.yaml
+++ b/jenkins/gerrit-mvn-plugin-github.yaml
@@ -3,6 +3,7 @@
     repo: github
     branch:
       - master
+      - stable-3.4
       - stable-3.3
       - stable-3.2
       - stable-3.1