Add 'release/2018.8.1' branch to repos

Fixes: PROD-23153 (PROD:23153)

Change-Id: I9972e0cb9065dd1fdddde6cd195aef72c9abfd03
diff --git a/jenkins/client/job/git-mirrors/downstream/pipelines.yml b/jenkins/client/job/git-mirrors/downstream/pipelines.yml
index 271a725..17611cb 100644
--- a/jenkins/client/job/git-mirrors/downstream/pipelines.yml
+++ b/jenkins/client/job/git-mirrors/downstream/pipelines.yml
@@ -8,8 +8,8 @@
       - name: pipeline-library
         downstream: mcp-ci/pipeline-library
         upstream: "${_param:gerrit_pipeline_library_repo}"
-        branches: master
+        branches: "master,release/2018.8.1"
       - name: mk-pipelines
         downstream: mk/mk-pipelines
         upstream: "${_param:gerrit_mk_pipelines_repo}"
-        branches: master
+        branches: "master,release/2018.8.1"