`skaffold init` erroneously thinks there are unused builder configs

[nkubala]

Running skaffold init on a modified version of the k8s Guestbook example, I'm prompted for the Dockerfile/k8s.yaml pairing as usual, and the skaffold.yaml I get at the end is what I want. However, I'm also getting a warning:

WARN[0001] unused builder configs found in repository: [{php-redis/Dockerfile} {redis-slave/Dockerfile}] 

➜  guestbook git:(master) ✗ skaffold init
? Choose the builder to build image gcr.io/nkubala-demo/gb-frontend Docker (php-redis/Dockerfile)
? Choose the builder to build image k8s.gcr.io/redis None (image not built from these sources)
? Choose the builder to build image gcr.io/nkubala-demo/gb-redisslave Docker (redis-slave/Dockerfile)
WARN[0001] unused builder configs found in repository: [{php-redis/Dockerfile} {redis-slave/Dockerfile}] 
apiVersion: skaffold/v1beta14
kind: Config
build:
  artifacts:
  - image: gcr.io/nkubala-demo/gb-frontend
    context: php-redis
  - image: gcr.io/nkubala-demo/gb-redisslave
    context: redis-slave
deploy:
  kubectl:
    manifests:
    - k8s/frontend-deployment.yaml
    - k8s/frontend-service.yaml
    - k8s/redis-master-deployment.yaml
    - k8s/redis-master-service.yaml
    - k8s/redis-slave-deployment.yaml
    - k8s/redis-slave-service.yaml