Build virtualhost module on stable-3.13

Change-Id: Iee771cc5c270e99e844d84ebaf5d177525df9840
diff --git a/jenkins/gerrit-bazel-module-virtualhost.yaml b/jenkins/gerrit-bazel-module-virtualhost.yaml
index 6e535d3..e8854fc 100644
--- a/jenkins/gerrit-bazel-module-virtualhost.yaml
+++ b/jenkins/gerrit-bazel-module-virtualhost.yaml
@@ -11,3 +11,4 @@
       - 'module-{name}-gh-bazel-{branch}':
           branch:
             - master
+            - stable-3.13