vendor: update github.com/spf13/cobra to master

vendor/github.com/spf13/cobra/doc/man_docs.go

@@ -20,6 +20,7 @@ import (
 	"os"
 	"path/filepath"
 	"sort"
+	"strconv"
 	"strings"
 	"time"
 
@@ -87,7 +88,7 @@ type GenManTreeOptions struct {
 
 // GenManHeader is a lot like the .TH header at the start of man pages. These
 // include the title, section, date, source, and manual. We will use the
-// current time if Date if unset and will use "Auto generated by spf13/cobra"
+// current time if Date is unset and will use "Auto generated by spf13/cobra"
 // if the Source is unset.
 type GenManHeader struct {
 	Title   string
@@ -104,14 +105,16 @@ func GenMan(cmd *cobra.Command, header *GenManHeader, w io.Writer) error {
 	if header == nil {
 		header = &GenManHeader{}
 	}
-	fillHeader(header, cmd.CommandPath())
+	if err := fillHeader(header, cmd.CommandPath()); err != nil {
+		return err
+	}
 
 	b := genMan(cmd, header)
 	_, err := w.Write(md2man.Render(b))
 	return err
 }
 
-func fillHeader(header *GenManHeader, name string) {
+func fillHeader(header *GenManHeader, name string) error {
 	if header.Title == "" {
 		header.Title = strings.ToUpper(strings.Replace(name, " ", "\\-", -1))
 	}
@@ -120,12 +123,20 @@ func fillHeader(header *GenManHeader, name string) {
 	}
 	if header.Date == nil {
 		now := time.Now()
+		if epoch := os.Getenv("SOURCE_DATE_EPOCH"); epoch != "" {
+			unixEpoch, err := strconv.ParseInt(epoch, 10, 64)
+			if err != nil {
+				return fmt.Errorf("invalid SOURCE_DATE_EPOCH: %v", err)
+			}
+			now = time.Unix(unixEpoch, 0)
+		}
 		header.Date = &now
 	}
 	header.date = (*header.Date).Format("Jan 2006")
 	if header.Source == "" {
 		header.Source = "Auto generated by spf13/cobra"
 	}
+	return nil
 }
 
 func manPreamble(buf *bytes.Buffer, header *GenManHeader, cmd *cobra.Command, dashedName string) {