Build websession-flatfile on stable-3.1{3,4} and master

Change-Id: I0af5724165ce07f1165429f9f157ad3fa4152218

jenkins/gerrit-bazel-plugin-websession-flatfile.yaml

diff --git a/jenkins/gerrit-bazel-plugin-websession-flatfile.yaml b/jenkins/gerrit-bazel-plugin-websession-flatfile.yaml
index 5aaa93f..d22f394 100644
--- a/jenkins/gerrit-bazel-plugin-websession-flatfile.yaml
+++ b/jenkins/gerrit-bazel-plugin-websession-flatfile.yaml
@@ -1,11 +1,15 @@
 - project:
     name: websession-flatfile
     jobs:
+      - 'plugin-{name}-bazel-{branch}':
+          branch:
+            - master
       - 'plugin-{name}-bazel-{branch}-{gerrit-branch}':
           branch:
             - master
           gerrit-branch:
-            - master
+            - stable-3.14
+            - stable-3.13
             - stable-3.12
             - stable-3.11
       - 'plugin-{name}-verifier'