move onbuild hook to post_build

hooks/build

@@ -1,14 +0,0 @@
-#!/bin/bash
-set -exuo pipefail
-
-docker build -t $DOCKER_REPO:$DOCKER_TAG .
-# build onbuild
-docker build --build-arg BASE_IMAGE=$DOCKER_REPO:$DOCKER_TAG -t ${DOCKER_REPO}-onbuild:$DOCKER_TAG .
-
-for V in master $stable; do
-
-    docker build --build-arg JUPYTERHUB_VERSION=$V -t $DOCKER_REPO:$V .
-done
-
-echo "tagging $IMAGE_NAME"
-docker tag $DOCKER_REPO:$stable $IMAGE_NAME

hooks/post_build

@@ -0,0 +1,4 @@
+#!/bin/bash
+set -exuo pipefail
+
+docker build --build-arg BASE_IMAGE=$DOCKER_REPO:$DOCKER_TAG -t ${DOCKER_REPO}-onbuild:$DOCKER_TAG onbuild