Build reviewers plugin for 3.9 and 3.10

Also fix build for Gerrit 3.8 to use the stable-3.8 branch

Change-Id: Ib79ee3b5b99ddaeccaf0e3cbfb829884c5b0d302
diff --git a/jenkins/gerrit-bazel-plugin-reviewers.yaml b/jenkins/gerrit-bazel-plugin-reviewers.yaml
index e7af937..4cad847 100644
--- a/jenkins/gerrit-bazel-plugin-reviewers.yaml
+++ b/jenkins/gerrit-bazel-plugin-reviewers.yaml
@@ -4,8 +4,6 @@
       - 'plugin-{name}-bazel-{branch}':
           branch:
             - master
-      - 'plugin-{name}-bazel-{branch}-{gerrit-branch}':
-          branch:
-            - master
-          gerrit-branch:
             - stable-3.8
+            - stable-3.9
+            - stable-3.10