Build simple-submit-rules against gerrit stable-3.6

Bug: Issue 15831
Change-Id: I880cacf73cba4fe3ec4ce1479f0cd24e81a11b00
diff --git a/jenkins/gerrit-bazel-plugin-simple-submit-rules.yaml b/jenkins/gerrit-bazel-plugin-simple-submit-rules.yaml
index c4445d9..21d1c00 100644
--- a/jenkins/gerrit-bazel-plugin-simple-submit-rules.yaml
+++ b/jenkins/gerrit-bazel-plugin-simple-submit-rules.yaml
@@ -9,5 +9,6 @@
             - master
           gerrit-branch:
             - master
+            - stable-3.6
             - stable-3.5
             - stable-3.4