Build login-redirect 'master' against gerrit stable-3.8

Change-Id: I3fd6f2b4b12e068ea94db63bb58420044931e126
diff --git a/jenkins/gerrit-bazel-plugin-login-redirect.yaml b/jenkins/gerrit-bazel-plugin-login-redirect.yaml
index 656d8b3..d379967 100644
--- a/jenkins/gerrit-bazel-plugin-login-redirect.yaml
+++ b/jenkins/gerrit-bazel-plugin-login-redirect.yaml
@@ -7,6 +7,7 @@
             - master
           gerrit-branch:
             - master
+            - stable-3.8
             - stable-3.7
             - stable-3.6
             - stable-3.5