Add missing bazel-slave image to the list

The bazel-slave image was missing in the list of images
to rebuild.

Change-Id: I10ac104902fecb32f52793d4d0abd2228f5cd2d8
diff --git a/jenkins-docker/Makefile b/jenkins-docker/Makefile
index bfafb17..0c56fca 100644
--- a/jenkins-docker/Makefile
+++ b/jenkins-docker/Makefile
@@ -1,4 +1,4 @@
-SLAVE_DIRS ?= slave-debian slave-chrome slave-node-wct slave-bazel-nocache slave-bazel-docker slave-sbt slave-mvn slave-release slave-python3 slave-jekyll
+SLAVE_DIRS ?= slave-debian slave-chrome slave-node-wct slave-bazel-nocache slave-bazel slave-bazel-docker slave-sbt slave-mvn slave-release slave-python3 slave-jekyll
 ALL_DIRS ?= master bazel-cache $(SLAVE_DIRS)
 NO_CACHE ?= true