Build 'websession-broker' master against Gerrit 'stable-3.7' branch

Change-Id: I5f9e791e202348369b118cd4d43fdc7e99439b11
diff --git a/jenkins/gerrit-bazel-plugin-websession-broker.yaml b/jenkins/gerrit-bazel-plugin-websession-broker.yaml
index aa1caf8..922a45b 100644
--- a/jenkins/gerrit-bazel-plugin-websession-broker.yaml
+++ b/jenkins/gerrit-bazel-plugin-websession-broker.yaml
@@ -6,6 +6,7 @@
             - master
           gerrit-branch:
             - master
+            - stable-3.7
             - stable-3.6
       - 'plugin-{name}-bazel-{branch}':
           branch: