Build virtualhost module against stable-3.8 branch

Change-Id: I1f658217e999637d4de894f4fff7e8e46a3ebd08
diff --git a/jenkins/gerrit-bazel-module-virtualhost.yaml b/jenkins/gerrit-bazel-module-virtualhost.yaml
index 3bac49c..83b4906 100644
--- a/jenkins/gerrit-bazel-module-virtualhost.yaml
+++ b/jenkins/gerrit-bazel-module-virtualhost.yaml
@@ -7,3 +7,4 @@
             - master
           gerrit-branch:
             - master
+            - stable-3.8