Will SEO modify the robots.txt?

Hi,

WordPress version: 3.5
WordPress SEO version: 1.3.3

I expected the plugin to do this:

I changed to use SEO sitemap instead of another plugin Google XML Sitemaps.
But I found SEO will not add the sitemap link into robots.txt. But Google XML Sitemaps will.

Is there any option to let SEO add the sitemap link to robots.txt?
Thanks

https://www.ads-software.com/extend/plugins/wordpress-seo/