Build importer plugin on Gerrit 2.15

Change-Id: Id22b00aed9ca8c08701267c3b8da3a3ac30e9369
diff --git a/jenkins/gerrit-buck-bazel-plugin-importer.yaml b/jenkins/gerrit-buck-bazel-plugin-importer.yaml
index fb36611..78de23a 100644
--- a/jenkins/gerrit-buck-bazel-plugin-importer.yaml
+++ b/jenkins/gerrit-buck-bazel-plugin-importer.yaml
@@ -8,5 +8,6 @@
             - stable-2.11
       - 'plugin-{name}-bazel-{branch}':
           branch:
+            - stable-2.15
             - stable-2.14
             - master