Update to use go modules (#671)

This includes updates to CI config, vendor files, etc.
I've hard-coded the k8s depedency at 1.13.4 to keep it inline with what
we currently have and to make sure a another run of `go mod tidy`
doesn't accidentally update it to an unexpected version.

Thanks to hectorj2f for carrying this along.

vendor/k8s.io/api/core/v1/types.go

@@ -2920,6 +2920,7 @@ type PodSpec struct {
 	RuntimeClassName *string `json:"runtimeClassName,omitempty" protobuf:"bytes,29,opt,name=runtimeClassName"`
 	// EnableServiceLinks indicates whether information about services should be injected into pod's
 	// environment variables, matching the syntax of Docker links.
+	// Optional: Defaults to true.
 	// +optional
 	EnableServiceLinks *bool `json:"enableServiceLinks,omitempty" protobuf:"varint,30,opt,name=enableServiceLinks"`
 }

vendor/k8s.io/api/core/v1/types_swagger_doc_generated.go

@@ -1540,7 +1540,7 @@ var map_PodSpec = map[string]string{
 	"dnsConfig":                     "Specifies the DNS parameters of a pod. Parameters specified here will be merged to the generated DNS configuration based on DNSPolicy.",
 	"readinessGates":                "If specified, all readiness gates will be evaluated for pod readiness. A pod is ready when all its containers are ready AND all conditions specified in the readiness gates have status equal to \"True\" More info: https://github.com/kubernetes/community/blob/master/keps/sig-network/0007-pod-ready%2B%2B.md",
 	"runtimeClassName":              "RuntimeClassName refers to a RuntimeClass object in the node.k8s.io group, which should be used to run this pod.  If no RuntimeClass resource matches the named class, the pod will not be run. If unset or empty, the \"legacy\" RuntimeClass will be used, which is an implicit class with an empty definition that uses the default runtime handler. More info: https://github.com/kubernetes/community/blob/master/keps/sig-node/0014-runtime-class.md This is an alpha feature and may change in the future.",
-	"enableServiceLinks":            "EnableServiceLinks indicates whether information about services should be injected into pod's environment variables, matching the syntax of Docker links.",
+	"enableServiceLinks":            "EnableServiceLinks indicates whether information about services should be injected into pod's environment variables, matching the syntax of Docker links. Optional: Defaults to true.",
 }
 
 func (PodSpec) SwaggerDoc() map[string]string {