add missing import

Author: techknowlogick

routers/web/admin/users.go

@@ -22,6 +22,7 @@ import (
 	"code.gitea.io/gitea/modules/optional"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/templates"
+	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/modules/web"
 	"code.gitea.io/gitea/routers/web/explore"
 	user_setting "code.gitea.io/gitea/routers/web/user/setting"