Build Scala scripting for Gerrit v2.15

Change-Id: I939b54d198ea60af37bc923f57ce535d162e57ca
diff --git a/jenkins/gerrit-buck-bazel-plugin-scala-provider.yaml b/jenkins/gerrit-buck-bazel-plugin-scala-provider.yaml
index bf4d294..5402e0f 100644
--- a/jenkins/gerrit-buck-bazel-plugin-scala-provider.yaml
+++ b/jenkins/gerrit-buck-bazel-plugin-scala-provider.yaml
@@ -11,4 +11,5 @@
             - master
           gerrit-branch:
             - master
+            - stable-2.15
             - stable-2.14