commands: Use short date format in CLI docs

To make it possible to compare the output.

See #4598

commands/gendoc.go

@@ -57,7 +57,7 @@ for rendering in Hugo.`,
 				return err
 			}
 		}
-		now := time.Now().Format(time.RFC3339)
+		now := time.Now().Format("2006-01-02")
 		prepender := func(filename string) string {
 			name := filepath.Base(filename)
 			base := strings.TrimSuffix(name, path.Ext(name))