replace deprecated io/ioutil with os and io for cmd

cmd/gendocs/gen_kubectl_docs.go

@@ -19,7 +19,7 @@ package main
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"os"
 
 	"github.com/spf13/cobra/doc"
@@ -47,6 +47,6 @@ func main() {
 	// Set environment variables used by kubectl so the output is consistent,
 	// regardless of where we run.
 	os.Setenv("HOME", "/home/username")
-	kubectl := cmd.NewKubectlCommand(cmd.KubectlOptions{IOStreams: genericclioptions.IOStreams{In: bytes.NewReader(nil), Out: ioutil.Discard, ErrOut: ioutil.Discard}})
+	kubectl := cmd.NewKubectlCommand(cmd.KubectlOptions{IOStreams: genericclioptions.IOStreams{In: bytes.NewReader(nil), Out: io.Discard, ErrOut: io.Discard}})
 	doc.GenMarkdownTree(kubectl, outDir)
 }