Fix task plugin branch configuration

task plugin now has stable-3.2 and stable-3.3 branches, but uses master
for stable-3.4 support still.

Change-Id: I2dced85bafbff7461407461558755906a3f59c84
diff --git a/jenkins/gerrit-bazel-plugin-task.yaml b/jenkins/gerrit-bazel-plugin-task.yaml
index de08214..0514dff 100644
--- a/jenkins/gerrit-bazel-plugin-task.yaml
+++ b/jenkins/gerrit-bazel-plugin-task.yaml
@@ -6,8 +6,10 @@
             - master
           gerrit-branch:
             - master
-            - stable-3.2
+            - stable-3.4
       - 'plugin-{name}-bazel-{branch}':
           branch:
             - master
+            - stable-3.3
+            - stable-3.2
             - stable-2.16