Merge pull request tektoncd#755 from nikhil-thomas/fix/test-failure

Replace busybox image url

openshift/release/update-to-head.sh

@@ -37,7 +37,7 @@ fi
 find . -type f -name '*.go' -o -name '*.yaml' | \
     xargs -P6 -L1 -r sed -E -i \
           -e 's,image: ubuntu$,image: public.ecr.aws/ubuntu/ubuntu:latest,' -e 's,"ubuntu","public.ecr.aws/ubuntu/ubuntu",g' \
-          -e 's,"busybox","mirror.gcr.io/library/busybox",g' -e 's,image: busybox$,image: mirror.gcr.io/library/busybox,'
+          -e 's,"busybox","gcr.io/google-containers/busybox",g' -e 's,image: busybox$,image: gcr.io/google-containers/busybox,'
 
 git commit -a -m ":robot: Switching image from docker.io to public cloud providers registry"