Warm-up bazel cache for stable-3.0 branch

Change-Id: Icf3724705300195469018621758220690a7dccb5
diff --git a/jenkins-docker/slave-bazel/Dockerfile b/jenkins-docker/slave-bazel/Dockerfile
index bf05e41..d4a48ed 100644
--- a/jenkins-docker/slave-bazel/Dockerfile
+++ b/jenkins-docker/slave-bazel/Dockerfile
@@ -9,6 +9,7 @@
     ./tools/setup_gjf.sh 1.7 && \
     ( bazel build //... || true ) && \
     git checkout -f stable-2.16 && git submodule update --init && ( bazel build //... || true ) && \
+    git checkout -f stable-3.0 && git submodule update --init && ( bazel build //... || true ) && \
     git checkout -f master && git submodule update --init && ( bazel build //... || true ) && \
     cd /tmp/gerrit && mv tools/format ~ && \
     rm -Rf /tmp/gerrit'