Fix cli command restore-repo: "units" should be parsed as StringSlice

Author: wxiaoguang

cmd/restore_repo.go

@@ -37,10 +37,10 @@ var CmdRestoreRepository = cli.Command{
 			Value: "",
 			Usage: "Restore destination repository name",
 		},
-		cli.StringFlag{
+		cli.StringSliceFlag{
 			Name:  "units",
-			Value: "",
-			Usage: `Which items will be restored, one or more units should be separated as comma.
+			Value: nil,
+			Usage: `Which items will be restored, one or more units should be repeated with this flag.
 wiki, issues, labels, releases, release_assets, milestones, pull_requests, comments are allowed. Empty means all units.`,
 		},
 		cli.BoolFlag{