Build metrics-reporter-prometheus on stable-3.1[1-3]

Change-Id: I9c7c7a97889584be575ee66b04046fbe856f45d1

jenkins/gerrit-bazel-plugin-metrics-reporter-prometheus.yaml

diff --git a/jenkins/gerrit-bazel-plugin-metrics-reporter-prometheus.yaml b/jenkins/gerrit-bazel-plugin-metrics-reporter-prometheus.yaml
index c8baa6a..2edc4d5 100644
--- a/jenkins/gerrit-bazel-plugin-metrics-reporter-prometheus.yaml
+++ b/jenkins/gerrit-bazel-plugin-metrics-reporter-prometheus.yaml
@@ -4,11 +4,11 @@
       - 'plugin-{name}-bazel-{branch}':
           branch:
             - master
+            - stable-3.13
+            - stable-3.12
+            - stable-3.11
       - 'plugin-{name}-bazel-{branch}-{gerrit-branch}':
           branch:
             - master
           gerrit-branch:
             - stable-3.14
-            - stable-3.13
-            - stable-3.12
-            - stable-3.11