Build avatar-gravatar plugin on its own stable-3.0 branch

Change-Id: I9f7d0cdf2cd5f8aad7ad3b5ea9cf06abe3f95f4c
diff --git a/jenkins/gerrit-bazel-plugin-avatars-gravatar.yaml b/jenkins/gerrit-bazel-plugin-avatars-gravatar.yaml
index f055cfc..aa4a325 100644
--- a/jenkins/gerrit-bazel-plugin-avatars-gravatar.yaml
+++ b/jenkins/gerrit-bazel-plugin-avatars-gravatar.yaml
@@ -8,7 +8,7 @@
             - master
             - stable-3.2
             - stable-3.1
-            - stable-3.0
       - 'plugin-{name}-bazel-{branch}':
           branch:
+            - stable-3.0
             - stable-2.16