Build uploadvalidator master against Gerrit stable-3.13

Change-Id: I8d98bb18af7b1f2850febae997c7dc770dd95fdc
diff --git a/jenkins/gerrit-bazel-plugin-uploadvalidator.yaml b/jenkins/gerrit-bazel-plugin-uploadvalidator.yaml
index c3465dd..8376da9 100644
--- a/jenkins/gerrit-bazel-plugin-uploadvalidator.yaml
+++ b/jenkins/gerrit-bazel-plugin-uploadvalidator.yaml
@@ -10,4 +10,5 @@
           branch:
             - master
           gerrit-branch:
+            - stable-3.13
             - stable-3.12