Error, Is Docker a pre-requisite for dev?

Command: `make verify`

Output:

Verifying hack/make-rules/../../hack/verify-api-reference-docs.sh
Note: This assumes that swagger spec has been updated. Please run hack/update-swagger-spec.sh to ensure that.
Generating API reference docs for group versions: v1 admissionregistration.k8s.io/v1alpha1 apps/v1beta1 apps/v1beta2 authentication.k8s.io/v1 authentication.k8s.io/v1beta1 authorization.k8s.io/v1 authorization.k8s.io/v1beta1 autoscaling/v1 autoscaling/v2beta1 batch/v1 batch/v1beta1 batch/v2alpha1 certificates.k8s.io/v1beta1 extensions/v1beta1 networking.k8s.io/v1 policy/v1beta1 rbac.authorization.k8s.io/v1 rbac.authorization.k8s.io/v1beta1 rbac.authorization.k8s.io/v1alpha1 scheduling.k8s.io/v1alpha1 settings.k8s.io/v1alpha1 storage.k8s.io/v1beta1 storage.k8s.io/v1, at dirs: /go/src/k8s.io/kubernetes/vendor/k8s.io/api/core/v1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/admissionregistration/v1alpha1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/apps/v1beta1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/apps/v1beta2 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/authentication/v1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/authentication/v1beta1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/authorization/v1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/authorization/v1beta1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/autoscaling/v1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/autoscaling/v2beta1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/batch/v1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/batch/v1beta1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/batch/v2alpha1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/certificates/v1beta1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/extensions/v1beta1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/networking/v1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/policy/v1beta1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/rbac/v1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/rbac/v1beta1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/rbac/v1alpha1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/scheduling/v1alpha1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/settings/v1alpha1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/storage/v1beta1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/storage/v1
Reading swagger spec from: /go/src/k8s.io/kubernetes/api/swagger-spec
Generating the docs at: /go/src/k8s.io/kubernetes/_tmp/api-reference
Generating api reference docs at /go/src/k8s.io/kubernetes/_output/generated_html
/go/src/k8s.io/kubernetes/hack/lib/swagger.sh: line 115: docker: command not found
!!! [0914 07:48:51] Call tree:
!!! [0914 07:48:51]  1: ./hack/update-api-reference-docs.sh:50 kube::swagger::gen_api_ref_docs(...)
FAILED   hack/make-rules/../../hack/verify-api-reference-docs.sh	3s

Error 2:
Verifying hack/make-rules/../../hack/verify-federation-api-reference-docs.sh
Note: This assumes that swagger spec has been updated. Please run hack/update-federation-swagger-spec.sh to ensure that.
Generating API reference docs for group versions: federation/v1beta1 v1 extensions/v1beta1, at dirs: /go/src/k8s.io/kubernetes/federation/apis/federation/v1beta1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/core/v1 /go/src/k8s.io/kubernetes/vendor/k8s.io/api/extensions/v1beta1
Reading swagger spec from: /go/src/k8s.io/kubernetes/federation/apis/swagger-spec
Generating the docs at: /go/src/k8s.io/kubernetes/_tmp_federation/api-reference
Generating api reference docs at /go/src/k8s.io/kubernetes/_output/generated_html
/go/src/k8s.io/kubernetes/hack/lib/swagger.sh: line 115: docker: command not found
!!! [0914 08:02:36] Call tree:
!!! [0914 08:02:36] 1: ./hack/update-federation-api-reference-docs.sh:48 kube::swagger::gen_api_ref_docs(...)
FAILED hack/make-rules/../../hack/verify-federation-api-reference-docs.sh 1s
Verifying hack/make-rules/../../hack/verify-federation-generated-swagger-docs.sh
+++ [0914 08:02:59] Building the toolchain targets:
k8s.io/kubernetes/hack/cmd/teststale
k8s.io/kubernetes/vendor/github.com/jteeuwen/go-bindata/go-bindata
+++ [0914 08:03:00] Generating bindata:
test/e2e/generated/gobindata_util.go
/go/src/k8s.io/kubernetes /go/src/k8s.io/kubernetes/test/e2e/generated
/go/src/k8s.io/kubernetes/test/e2e/generated
+++ [0914 08:03:02] Building go targets for linux/amd64:
cmd/genswaggertypedocs
Generating swagger type docs for federation/v1beta1 at federation/apis/federation/v1beta1
diffing /go/src/k8s.io/kubernetes/federation against freshly generated swagger type documentation
/go/src/k8s.io/kubernetes/federation up to date.