[Security] Bump k8s.io/client-go from 0.15.7 to 0.20.0

Bumps [k8s.io/client-go](https://github.com/kubernetes/client-go) from 0.15.7 to 0.20.0. **This update includes security fixes.**
- [Release notes](https://github.com/kubernetes/client-go/releases)
- [Changelog](https://github.com/kubernetes/client-go/blob/master/CHANGELOG.md)
- [Commits](https://github.com/kubernetes/client-go/compare/v0.15.7...v0.20.0)

main.go

@@ -1,15 +1,17 @@
 package main
 
 import (
+	"context"
 	"flag"
+	"log"
+	"strings"
+	"time"
+
 	"k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/api/resource"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/client-go/kubernetes"
 	"k8s.io/client-go/rest"
-	"log"
-	"strings"
-	"time"
 )
 
 type args struct {
@@ -21,6 +23,7 @@ type args struct {
 func main() {
 	args := parseArgs()
 
+	ctx := context.Background()
 	config, err := rest.InClusterConfig()
 	if err != nil {
 		panic(err.Error())
@@ -52,7 +55,7 @@ func main() {
 	excludedNS := strings.Split(*args.ExcludedNS, ",")
 
 	for {
-		namespaces, err := clientset.CoreV1().Namespaces().List(metav1.ListOptions{})
+		namespaces, err := clientset.CoreV1().Namespaces().List(ctx, metav1.ListOptions{})
 		if err != nil {
 			panic(err)
 		}
@@ -60,12 +63,12 @@ func main() {
 		for _, ns := range namespaces.Items {
 			if !nsExcluded(ns.Name, excludedNS) {
 				log.Printf("Checking for LimitRange named extreme-request-defaults in namespace '%v'\n", ns.Name)
-				if limitRanges, err := clientset.CoreV1().LimitRanges(ns.Name).List(metav1.ListOptions{FieldSelector: "metadata.name=extreme-request-defaults"}); err != nil {
+				if limitRanges, err := clientset.CoreV1().LimitRanges(ns.Name).List(ctx, metav1.ListOptions{FieldSelector: "metadata.name=extreme-request-defaults"}); err != nil {
 					panic(err)
 				} else {
 					if len(limitRanges.Items) == 0 {
 						log.Printf("Trying to create LimitRange\n")
-						if _, err := clientset.CoreV1().LimitRanges(ns.Name).Create(&limitRange); err != nil {
+						if _, err := clientset.CoreV1().LimitRanges(ns.Name).Create(ctx, &limitRange, metav1.CreateOptions{}); err != nil {
 							log.Printf("Unable to create LimitRange in namespace '%v': Error: %v\n", ns.Name, err)
 						} else {
 							log.Printf("LimitRange extreme-request-defaults created in namespace '%v'\n", ns.Name)