sort custom column print flags

Kubernetes-commit: 36ed148761cb5a30c21b45a64d95cabd1a9d07ff

pkg/cmd/get/customcolumn_flags.go

@@ -19,6 +19,7 @@ package get
 import (
 	"fmt"
 	"os"
+	"sort"
 	"strings"
 
 	"github.com/spf13/cobra"
@@ -45,6 +46,7 @@ func (f *CustomColumnsPrintFlags) AllowedFormats() []string {
 	for format := range columnsFormats {
 		formats = append(formats, format)
 	}
+	sort.Strings(formats)
 	return formats
 }