Build stable-3.1{2,3,4} branches of avatars-external

Change-Id: I9f5750af2c5c2736c27e45250c836824b5245cfe

jenkins/gerrit-bazel-plugin-avatars-external.yaml

diff --git a/jenkins/gerrit-bazel-plugin-avatars-external.yaml b/jenkins/gerrit-bazel-plugin-avatars-external.yaml
index 34eb944..c30fb7a 100644
--- a/jenkins/gerrit-bazel-plugin-avatars-external.yaml
+++ b/jenkins/gerrit-bazel-plugin-avatars-external.yaml
@@ -1,8 +1,9 @@
 - project:
     name: avatars-external
     jobs:
-      - 'plugin-{name}-bazel-{branch}-{gerrit-branch}':
+      - 'plugin-{name}-bazel-{branch}':
           branch:
-            - master
-          gerrit-branch:
+            - stable-3.12
+            - stable-3.13
+            - stable-3.14
             - master