Build the readonly plugin on stable-2.16

Change-Id: I4dbff3e91d1f36fd017558680b35726bbb1f5c92
diff --git a/jenkins/gerrit-buck-bazel-plugin-readonly.yaml b/jenkins/gerrit-buck-bazel-plugin-readonly.yaml
index 26a0566..a28c2f4 100644
--- a/jenkins/gerrit-buck-bazel-plugin-readonly.yaml
+++ b/jenkins/gerrit-buck-bazel-plugin-readonly.yaml
@@ -4,5 +4,6 @@
       - 'plugin-{name}-bazel-{branch}':
           branch:
             - master
+            - stable-2.16
             - stable-2.15
-            - stable-2.14
\ No newline at end of file
+            - stable-2.14