fix a typo

when i was using:
docker search --automated -s 3 nginx
told me:
Flag --automated has been deprecated, use --filter=automated=true instead
Flag --stars has been deprecated, use --filter=stars=3 instead
and when i use:
docker search --filter=automated=true --filter=stars=3 nginx
told me:
Error response from daemon: Invalid filter 'automated'
and i found out that the correct command should be:
docker search --filter=is-automated=true --filter=stars=3 nginx

Signed-off-by: Pure White <daniel48@126.com>

cli/command/registry/search.go

@@ -52,7 +52,7 @@ func NewSearchCommand(dockerCli *command.DockerCli) *cobra.Command {
 	flags.BoolVar(&opts.automated, "automated", false, "Only show automated builds")
 	flags.UintVarP(&opts.stars, "stars", "s", 0, "Only displays with at least x stars")
 
-	flags.MarkDeprecated("automated", "use --filter=automated=true instead")
+	flags.MarkDeprecated("automated", "use --filter=is-automated=true instead")
 	flags.MarkDeprecated("stars", "use --filter=stars=3 instead")
 
 	return cmd