Kubectl "outdated" plugin

We use Kubernetes at work and I am mostly responsible for making it run smoothly. This means staying on top of new releases, libraries and tools that come out at a pace I've never experienced before, in any project.

To help with that, I wrote a kubectl plugin that finds outdated components in a Kubernetes cluster. The code can be found here.

It works like this.

First it goes through all deployments and daemonsets, collecting the images referenced in their containers.
For each container, search for a newer image tag in its repository. I currently support querying Docker Hub and Google Container Repository (you need gcloud for that).
Outputs which deployment or daemonset needs upgrading.

E.g. running it on a testing cluster I setup gives this output:

$> kubectl plugin outdated
Deployment:gitlab-ci/gitlab-runner                                                     gitlab/gitlab-runner:alpine-v9.5.0 -> v10.3.0             
Deployment:gitlab/gitlab-ce                                                                   gitlab/gitlab-ce:9.5.9-ce.0 -> 10.3.3-ce.0         
Deployment:gitlab/redis                                                                            bitnami/redis:3.2.8-r2 -> 4.0.6-r1            
Deployment:kube-system/dashboard                               gcr.io/google_containers/kubernetes-dashboard-amd64:v1.6.3 -> v1.8.1              
Deployment:kube-system/heapster                                            gcr.io/google_containers/heapster-amd64:v1.4.0 -> v1.5.0              
Deployment:kube-system/kube-dns                                    gcr.io/google_containers/k8s-dns-kube-dns-amd64:1.14.5 -> 1.14.7              
Deployment:kube-system/kube-dns                               gcr.io/google_containers/k8s-dns-dnsmasq-nanny-amd64:1.14.5 -> 1.14.7              
Deployment:kube-system/kube-dns                                     gcr.io/google_containers/k8s-dns-sidecar-amd64:1.14.5 -> 1.14.7              
Deployment:kube-system/monitoring-grafana                          gcr.io/google_containers/heapster-grafana-amd64:v4.4.1 -> v4.4.3              
Deployment:kube-system/monitoring-influxdb                        gcr.io/google_containers/heapster-influxdb-amd64:v1.1.1 -> v1.3.3              
DaemonSet:kube-system/calico-etcd                                                     gcr.io/google_containers/etcd:2.2.1 -> 3.1.11              
DaemonSet:kube-system/kube-proxy                                         gcr.io/google_containers/kube-proxy-amd64:v1.8.5 -> v1.10.0-alpha.1